Gravity measuring apparatus

Gravity measuring apparatus is disclosed. In the preferred and illustrated embodiment, an apparatus utilizing a balanced container floating in a liquid rises and falls according to variations in gravity. Such variations in position are coupled to a measuring apparatus. In one embodiment, a horizontal beam pivotally mounted at one end and connected to the float as its center and nearly balanced about the pivot support at one end is deflected as the float rises and falls. Movement thereof is connected to a multiplier which enlarges the movement by some scale factor convenient to the circumstances in the range of 100 to about 1,000 to form an enlarged deflection of the multiplier adjacent to a motorized recorder, thereby forming a usable output indicia. The multiplier includes a pivotally mounted, upstanding framework having counterbalances so that it can stand vertically above its pivot point and further incorporates a laterally extending arm to which movements of the horizontal beam are coupled, the length of the arm from the pivot compared to the length of the multiplier providing the ratio of multiplication desired.

BACKGROUND OF THE DISCLOSURE 
Gravity is considered to be a three-dimensional vector force. Utilizing an 
X, Y and Z-coordinate system, gravity can readily be defined as an 
attractive force between an object and the earth with the force having 
components in all three dimensions. If the coordinate system is 
conveniently defined at the center of the earth and the Y-axis is defined 
along the line between the earth and the object of interest, then the 
Y-component of gravity will be quite large compare to the X and 
Z-components. If they are conveniently defined as the north-south and 
east-west components (bringing into play the relatively well known surface 
coordinates on the earth), then those components are materially smaller. 
It will be appreciated that measurement of the Y or large component of 
gravity is extremely significant in certain scientific phenomena. 
One phenomena where gravity measurements of the earth are extremely helpful 
is in prospecting for minerals. The earth is not a homogeneous body. As a 
result, it is known that pattern variations in the measurement of the 
vertical component of gravity over a given geological region may very well 
show a set of variations which are coherently related to the geology of 
the region. As an example, large masses of iron ore create regional 
discontinuities in the measurements which, on proper interpretation, yield 
valuable information for determining the extent of the mass of iron ore in 
the earth. 
While regional variations in gravity occur, variations also occur at a 
given locale over long or short periods of time as a result of a variety 
of reasons including, as an example, movement of extraterrestrial bodies. 
Accordingly, a set of base measurements over a period of time are usually 
deemed necessary to have a fixed base measurement whereby mesurements 
taken in a large locale (for instance, in prospecting for various mineral 
deposits) are made so that all measurements can be referenced (by 
subtraction of time variations) to a common base station measurement to 
obtain time invariant measurements. To the extent that measurements at a 
given spot vary over a time interval, such variations are mathematically 
removed for the purpose of achieving a base station measurement taken in 
the locale. The present invention is a gravity meter which responds to 
variations in the vector component of gravity acting between the gravity 
meter and the earth and which converts such variations into a physical 
movement which can be measured and recorded on a time base chart. 
The present invention has as one of its advantages a gravity measuring 
system using a hydraulically damped mass which mass moves in response to 
gravity variations. Such damping fairly well eliminates instrument system 
induced variations as might occur with an undamped structure. The mass 
moves responsive to variations over a period of time with sufficient 
damping so that overshoot, oscillations or transducer errors are not 
induced. The apparatus achieves this by utilizing a gravity attracted mass 
in a liquid bath. The system is balanced by supporting the transducer mass 
from a horizontal beam of significant length, one end of the beam being 
mounted on a pivot mount to enable the beam to deflect. The beam is thus 
rotated around its pivot by the transducer mass. The slightly arcuate 
movement of the transducer mass as it rotates around the pivot point of 
the mounting beam is an excursion of only a few microns, and, therefore, 
angular distortion of the response is minimal. The beam and hydraulic 
damping system which receives the transducer mass is relatively simple in 
structure and is, therefore, relatively straightforward in mounting. This 
is particularly advantageous in initially setting up the equipment and 
adjusting it to maximum sensitivity by eliminating off-balance mounting 
and other distorting forces. 
An important feature of this apparatus is the multiplier which is 
incorporated. The multiplier is an apparatus which connects with the 
horizontal beam and enlarges movement thereof. The multiplier converts the 
relatively small movement of the transducer mass into a much larger 
movement by a scale factor of between approximately 100 to 1,000. This 
scale factor is controlled by sizing of the multiplier. Accordingly, it 
can be varied to a requisite value for the purpose of obtaining a 
different excursion in response to the transducer mass. The multiplier has 
as one feature the incorporation of a indicator disk mounted at its remote 
upper end. The indicator disk is observed in location by utilization of a 
photoelectric sensor and light bulb, thereby coupling movements of the 
indicator disk to a recording instrument. 
From the foregoing, it will be understood how the apparatus is able to 
respond to variations in the vertical component of gravity which are 
converted into excursions of significant amplitude. They are converted and 
placed in a form enabling recordal on a time base chart mechanism. 
BRIEF SUMMARY OF THE DISCLOSURE 
This disclosure is directed to a gravity measuring device utilizing a 
transducer mass having the form of a large, vented tank submerged in a 
fluid. The tank rises and falls in response to gravity attraction 
variations. The tank is connected to and supported from a horizontally 
mounted beam rested on a pivot at one end. The opposite end is free to 
move in response to variations of gravity. As the transducer mass rises or 
falls, the free end of the arm is moved. Its movement is supplied through 
a coupling mechanism to a muliplier means which is an upstanding column 
having a length of between about 100 to 1,000 times greater than the lever 
arm coupled to it to multiply the rather minute movements of the 
horizontal beam. The movements are observed through the use of an optical 
sensor system which located an indicator disk at the top end of the 
multiplier.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT 
Attention is directed to FIG. 1 of the drawings, where the numeral 10 
identifies the gravity measuring instrument of the present invention which 
is responsive to the vertical or Y-component of gravity. It responds to 
the component which acts along a line from the center of the earth to the 
measuring instruments. It will be observed that gravity is a 
three-dimensional vector having perpendicular components in the other two 
dimensions which are not measured by this instrument. This instrument 
measures the component of most significance. The gravity measuring 
instrument 10 is received in a housing which is generally shaped as an 
"L". It has metal plates 11 which cover it and support insulative material 
12. It rests or is supported on a floor 13. 
The floor 13 need not be any special surface. Ordinarily, a concrete slab 
will suffice. Other surfaces can also be used. The covering 11 is in the 
form of relatively thin plate material. Preferably, it provides shielding 
against penetration of the housing by electromagnetic radiation. This 
reduces errors in the operation of the equipment. The insulation material 
12 stabilizes the interior to a selected temperature level. It is 
preferably stable with fluctuations limited to about 1.0.degree. C. 
The housing 11 is supported by suitable frame members. The housing seals 
the interior against entry of light. It is not necessary to seal the 
interior against atmospheric fluctuations; they do not provide a an 
important source of error, although controlled pressure is more desirable. 
A pair of duplicate elongate brackets 14 extend in the housing, and they 
are supported on upstanding braces 15 and 16 shown in FIG. 1. The two 
L-shaped frame members are stationary and are spaced apart. They support 
equipment which will be described. They pass in front of and behind a 
cylindrical tank 17 filled with a liquid 18. Water is acceptable for the 
tank. Other fluids preferably have a reduced or minimal evaporation rate. 
The water 18 is normally prevented from evaporating by placing oil 19 on 
the surface of it to reduce evaporation to a minimum. 
The tank 17 is fairly large, having a capacity of a few liters. It 
terminates at a top shoulder 20 which includes a sharp, radially inwardly 
directed edge. This cooperates with the surface oil 19 to reduce 
evaporation, contact being maintained with the surface oil. 
As shown in FIG. 2 of the drawings, a nonwetting hood 21 spans the top. It 
has a central hole or opening to permit the equipment to operate through 
it. The hood 21 can be made of metal and is internally coated with a 
nonwetting material such as Teflon. 
The numeral 22 identifies a horizontal beam structure. Speaking generally, 
it is a fairly large framework having a maximum measure along its length 
and is relatively narrow through it. No particular ratio need be achieved. 
It is a framework formed of metal members as better shown in plan view in 
FIG. 6. FIG. 6 shows the horizontal beam 22 extending in the cabinet or 
housing which encloses it. It includes a back frame member 23 and a 
parallel front frame member 24 which are of equal length and parallel to 
one another. They support a transverse, centralized cross brace 25 
constructed with a pair of parallel rods which support a centrally located 
block which, in turn, connects to a hollow tube 26. The tube 26 is open to 
atmosphere and opens into the interior of a tank 27. The sensitive element 
of the present invention which functions as a transducer means is the tank 
27. The tank 27 is substantially closed, but it is open on the interior to 
receive a liquid 28. It is open to the exterior through the narrow conduit 
26. 
As viewed in FIG. 1, the horizontal beam 22 is pivotally mounted at one 
end. It is able to rotate about the pivot mounting. As it rises or falls, 
it moves the other end along an arc. Movement is initiated by gravity 
fluctuations acting on the tank 27. It functions as a buoyant element and 
is almost balanced. That is, it is almost balanced to zero buoyancy, 
taking into account the weight of the entire system. It is able to float 
and has a tendency to float slightly, this tendency being represented by a 
slight offset from perfect balancing of the buoyant forces. The tank 27 
thus responds to fluctuations in gravity. It is raised or lowered as 
gravity fluctuates over a period of time. 
The closed tank 27 is a float filled with a liquid 28 which has reduced 
specific gravity in comparison with the damping fluid 18. This adjusts the 
buoyancy so that the net buoyancy is slight. The buoyancy is nearly zero 
without being zero. If it were zero, no imbalance would occur, and the 
float would not rise or fall. Perfectly neutral buoyancy wuld be 
nonresponsive to time variant gravity. The conduit 26 is hollow and is 
open to atmosphere so that the tank 27 is open to atmosphere. This enables 
atmospheric variations in pressure to be supplied to the interior of the 
tank 28 to avoid relative pressurization of the tank. The tank 27 is 
floated within the bath and rises and falls with variations in gravity or 
vertical components of crustal surges. As the tank rises or falls, such 
variations are connected through the mounting stem 26 to the beam 22. 
The beam 22 is pivotally mounted. For a better understanding of this, 
attention is directed to FIG. 6 of the drawings which shows the beam 22 in 
greater detail. The beam 22 includes a counterbalance arm 30 and a 
counterbalance weight 31. They extend to the right of a pivot point. The 
remainder of the beam is to the left of the pivot point. The pivot point 
is the fulcrum around which the beam 22 rotates. Because the beam has 
significant width, it is desirable to utilize two pivot points which are 
on a common axis of rotation, as better shown in FIG. 7 of the drawings. 
There, the beam will be observed to include parallel frame members 23 and 
24 which join together at a transverse frame member 32 at the end of the 
beam. The frame member 32 supports a pin 33 which has a lower face which 
is pointed in a conic surface. It defines a point 34 at the lower tip 
which has an included angle which is relatively sharp in comparison with 
the mating component. The point 34 is received into a support block 35 
having a dished portion in the center which is a conic surface. The angle 
is relatively shallow. The point 34 is thus supported in the dished area 
with point contact. The point 34 is centered within the dished area by the 
shape of the conic surface. The support block 35 is supported on the fixed 
frame members 14. 
The horizontal frame member 32 supports a metal pin 36 which extends 
downwardly and terminates at a knife edge 37. The knife edge 37 is, when 
viewed on end, the lower apex of cut and polished surfaces terminating at 
the apex. Again, they describe an acute angle between them. A support 38 
is positioned on the frame 14 and has the form of a rectangular block 
having an upper face machined into a pair of sloping surfaces. The sloping 
surfaces come together at an angle which is greater than the acute angle 
of the knife edge 37. As an example, the knife edge 37 might be formed by 
a pair of faces inscribing an angle of about ninety degrees. The support 
means 38 receives the knife edge 37 in a pair of faces which define an 
angle larger than ninety degrees. As a result of this arrangement, the 
knife edge 37 makes line contact with the support surface below it. 
The knife edge 37 has a finite length as, for instance, a few millimeters. 
The support means 38 beneath it is sufficiently longer that the knife edge 
is able to move to the right or left, enabling insertion of the knife edge 
into the support surface. Moreover, it permits the equipment to be fixed 
against lateral movement whereby the point 34 is first positioned, and the 
knife edge is thereafter positioned. It will be appreciated that the knife 
edge 37, if extended through space, would pass through the point 34. This 
defines a common axis of rotation for the horizontal beam 22. 
As described to this juncture, the beam 22 pivots along a frictionless edge 
which is defined by the point 34 aligned with the extended knife edge 37. 
Movement to the left or right as viewed in FIG. 6 is not permitted. No 
binding occurs because the frame members 14 are sufficiently spaced from 
the apparatus to enable the point and edge supports shown in FIG. 7 to 
function freely without binding. 
Continuing with the description of the horizontal beam 22, it will be 
observed in FIG. 6 to incorporate an end frame member 40 parallel to and 
opposite the end transverse member 32. The members 32 and 40 are parallel, 
and they move with the unit as deflection occurs. The transverse frame 
member 40, being at the remote end, moves in an arc about the pivot point 
at the opposite end. When it rotates, it moves a long, thin marker 41 
which has a protruding tab 42. This is received in an eyelet 43, better 
shown in FIG. 5 of the drawings where the tab 42 protrudes through the 
eyelet 43. As the tab 42 is deflected upwardly or downwardly traveling 
about the pivot at the opposite end, it moves the eyelet 43. The eyelet 43 
is deflected upwardly or downwardly on rotation. When the eyelet 43 is 
contacted by the tab 42, it is pushed upwardly or downwardly. The eyelet 
is mounted so that movement occurs after contact, and, given the 
whisker-like construction of the marker 41, frictional drag is reduced to 
an insignificant amount. Drag is significantly eliminated by microseismic 
movement. 
As described to this juncture, changes in the vertical component of gravity 
raise and lower the tank 27 which serves as a transducer means responsive 
to gravity fluctuations. It moves in a liquid bath which damps its 
movement and is rigidly aligned by the mounting of the beam 22. The beam 
22 has moderate length, perhaps 2.0 meters or so, while the tank 27 
encloses a capacity of 2.0 liters, more or less. the tank is mounted at 
approximately the midpoint of the beam, and its movement, being in the 
range of microns, is multiplied by the ratio of the length of the beam to 
the lever arm to the mounting of the tank 27. This is approximately a 2:1 
multiplication. This multiplication is not critical. At this juncture, the 
range of movement is relatively small and difficult to work with. It is 
multiplied in a manner to be described by a factor ranging between about 
100 and 1,000-fold to yield a deflection of greater size. 
The frame member 14 supports an upstanding post 45 shown in FIG. 1. The 
post 45 is parallel to a similar post which is obscured in FIG. 1. The two 
posts terminate in surface areas similar to those shown in FIG. 7. One 
post terminates in a flat, dished surface having a conic cut terminating 
at a shallow point. The other post terminates at a pair of faces which are 
V-shaped to thereby define a surface receiving a knife edge. The equipment 
shown in FIG. 7 is duplicated to this extent. FIG. 6 discloses a shaft 48 
which supports an inserted pin 49 at one end and a similar pin 50 at the 
other end. The pins 49 and 50 terminate in the point and knife edge 
construction shown in FIG. 7 and are supported on the posts therebelow. 
This defines an axis of rotation for the shaft 48. The axis of rotation is 
below the shaft 48, not through it. The axis of rotation, being below the 
shaft, is the axis of rotation for the eyelet 43 previously mentioned. The 
precise location of the axis of rotation may be altered dependent on shaft 
construction and mounting. 
As shown in FIG. 1, the shaft 48 supports a circular weight 51 which is a 
weight centered on the shaft. In particular, the weight 51 is balanced to 
the right and left as viewed in FIG. 1. It supports four protruding arms 
52, 53, 54 and 55 which, in turn, each support weights 56, 57, 58 and 59 
on the respective shafts. The several weights are adjustable in location 
and are moved by rotating them, the several shafts being threaded. As the 
weights move on the threaded shafts, they can be moved outwardly or 
inwardly. When they are moved outwardly, they increase the torque which 
they cause, tilting the apparatus in that direction. The amount of weight 
is preferably symmetrical along the centerline of the equipment so that 
the weights 56 and 59 are balanced against one another. In like manner, 
the shafts 52 and 55 are constructed similarly, and the shafts, 
themselves, contribute to the fixed, nonadjustable weight in the 
structure. The aggregate weight is in the range of 5.0 to 30.0 kilograms, 
counting the centered, circular weight 51. This quantity of weight lends 
stability to the structure which is mounted on a knife edge for rotation. 
The several weights are adjustable and thereby permit calibration. 
Calibration is achieved when the multiplier apparatus is vertical. Any 
upright position which is stable is acceptable. Centering is desirable to 
permit wide fluctuations in either direction. 
FIG. 1 of the drawings discloses upstanding rods 60 in the center and rods 
61 and 62 on the outer edges, the three rods defining an upstanding 
pointer framework. The framework is light and fairly wide at the base, 
being in the range of 5.0 to 25.0 centimeters width in the preferred 
embodiment. Moreover, the frame member or rod 60 is forward of the other 
two rods as better shown in FIG. 3. The several vertical extending rods 
60, 61 and 62 are supported by various cross-bracing members 63 and 64 
which are added to provide structural rigidity. It will be observed that 
the three rods taper upwardly to intersect at a junction 65 where they are 
brazed or soldered together. If desired, the rod 60 can be duplicated by 
placing a similar rod supported on the center shaft 48 at the back end of 
the shaft to add a fourth leg. The upstanding structure is basically rigid 
and does not flex or bend. It is very important that the structure stand 
erect free of bending. Movement is coupled to the tip without bending. 
The several rods come together at the junction 65 and support an upstanding 
single rod 66. The rod 66 is relatively rigid, and it, in turn, supports 
an indicator disk 67. As shown in FIG. 3, the indicator disk 67 is 
immediately adjacent to a detector mechanism including a protruding arm 68 
which supports a light and a photocell in the structure. This is better 
understood by referring to FIG. 4 of the drawings. FIG. 4 shows an arcuate 
track 70 about the axis which is defined by the knife edge holding the 
multiplier apparatus vertically. The arcuate track 70 is a rectangular 
metal member which extends between end plates 71 and 72. They, in turn, 
support a lead screw 73. A carriage 74 travels along the lead screw by 
means of a motorized traveling nut which is obscured by the housing seen 
in FIG. 4. The traveling nut rotates clockwise or counterclockwise on the 
screw 73, moving the carriage 74 along the lead screw 73. As it travels, 
it engages the arcuate track 70 with rollers 75 on the bottom and 76 and 
77 which are above the track 70. The track 70 is curved as mentioned 
before. FIG. 4 slightly exaggerates its curvature for sake of clarity. The 
curvature is such as to require the carriage 74 to elongate slightly as 
the carriage moves toward the end frame members 71 and 72. The rollers 
maintain engagement so that the carriage is referenced to the curved track 
70. While its motive force is supplied via the lead screw 73, the lead 
screw 73 is, in turn, rotated by a motor 78. The motor 78 rotates 
clockwise or counterclockwise to thereby drive the carriage. The carriage 
elongates by permitting a sliding mounting bar 79 to extend slightly. 
Extension is in the millimeter range. 
The carriage 74 supports the rearwardly protruding arms 68 shown in FIG. 3. 
The disk 67 is a target for the apparatus. The disk 67 is visually 
detected by illuminating a lamp carried on the carriage. The lamp passes 
light through a small hole in the disk 67, and the light falls on a 
photocell. Ambient light is ordinarily excluded from the cabinet or 
housing. The carriage 74 thus follows the target disk 67 to the right or 
left. When the photosensitive device detects the light that passes through 
the hole, the carriage motor 78 is stopped. When the disk 67 moves, the 
carriage 74 travels with it. The carriage 74 thus travels in response to a 
circuit connected to the photosensitive device, the device being connected 
to an amplifier of a servoloop connected to the drive motor 78. Thus, the 
carriage 74 moves to the right and left. 
As shown in FIG. 3, chart paper 80 traveling from a supply spool 81 moves 
upwardly and is wrapped around an upper spool. The carriage 74 supports a 
marker 82 shown in FIG. 3 which preferably is an ink or ball point pen for 
marking on chart paper. Paper is supplied at a clocked rate so that its 
travel is regulated to some scale factor. Deflections marked on the chart 
are also marked against arbitrary scale calibrations on the chart which 
are used later to calibrate the gravity instrument. 
The disk is coupled by capacitance, reluctance or optical coupling. It is 
important to avoid coupling which drags the disk, a form of bias. The 
coupling is, therefore, minimal, being reduced by using small plates in a 
capacitive system, an aluminum disk in a magnetic system or a perforated 
disk in an optical system. Bias is further reduced by orienting the disk 
position detector system perpendicular to the plane of movement. In FIG. 
4, the disk 67 moves right or left, and the detection coupling is at right 
angles. 
The system as described to this juncture follows the indicator or target 
disk 67. It will be appreciated that it is not coupled in any way to 
create drag. So to speak, there is an infinite impedance coupling between 
the two. They are, in that sense, completely independent of one another, 
except that the carriage 74 follows the location of the target disk 66. 
Hunting or oscillations as a result of the movement of the carriage are 
held to a minimum. This can be achieved by utilizing a relatively small 
opening in the target 67. A larger target can be used, and a colored or 
optical filter placed in it to screen the light from the light bulb can be 
used. If desired, a particular wavelength of light can be used to trigger 
the photosensitive device which follows the light. As the target moves to 
the right or left, it cuts down on the light which falls on the photocell. 
As the photocell detects less light, it creates a signal which drives the 
motor 78. The motor 78, when driven, repositions the carriage 74 to 
increase the amount of light falling on the photocell. Another form of 
detector utilizes an aluminum disk mounted near a pair of spaced magnetic 
coils. The aluminum disk slightly responds to vary the reluctance of the 
two magnetic circuits so that a null is found at a centered position, or 
an unbalance is formed which, on amplification, will drive the motor. 
While this might be termed a magnetic coupling, the poor aluminum response 
prevents inductive drag or bias on the disk. 
In one embodiment of the present apparatus, the multiplication is at least 
100-fold. Multiplication is determined by the ratio of the length from the 
target disk 67 to its axis divided by the lever arm to the eyelet 43 shown 
in FIG. 5 from the same axis. While the multiplier arm might be quite 
heavy, nulling its weights to obtain a delicate balance when the device is 
being set up results in a highly sensitive multiplier. The multiplier does 
not drag or otherwise impede operation of the system. Rather, it responds 
in a way that enables the arm to be deflected free of frictional drag and 
other similar impediments. Again, drag is minimal in the direction of 
movement. The disk is not biased, reducing errors to a minimum. 
Preferably, the apparatus of the present invention is made of nonmagnetic 
material. It is preferably made of material which is relatively 
temperature stable. It is also made of material which ordinarily does not 
corrode on exposure to atmosphere. It is housed in a temperature 
stabilized container. The housing is preferably sealed against light to 
avoid radiation heating of the interior which will typically create 
unwanted air currents. Further, the present apparatus is formed of 
material which is reasonably strong and free of galling at the contact 
areas. This is particularly true for the knife edge and point support 
arrangement shown in FIG. 7. There, point loading and edge loading is 
fairly notable, and the surfaces are thus preferably made of nongalling 
alloys. 
The device of the present invention is used in the following manner. The 
beginning point is nulling the system. The float is nulled by first 
placing the float 27 in the bath 18. Its weight is adjusted by adding 
liquid 28 to it. After it is floating at a central and nearly neutral 
position, it is then ready to be used. This central or null position is 
achieved whereby the buoyancy of the tank, the weight of the beam 22, the 
offset provided by the counterbalance 31 and all other factors leave it 
nearly balanced in a horizontal posture with the float 27 clear of the 
walls of the tank 17 and fully submerged in the bath 18. The bath 18 does 
not evaporate as a result of the oil 19 placed on its surface. The liquid 
28 in the tank 27 does not evaporate because it has a very minimal surface 
area exposed to atmosphere. If desired, it can be topped off by adding oil 
to the surface to reduce evaporation. At this juncture, the equipment will 
function as a gravity meter. 
The beginning position requires a slightly buoyant offset from a perfect 
balance. Perfect balancing would make the float insensitive to gravity 
fluctuations. If the fluctuations are to be measured, the float must not 
be perfectly balanced so that it will move with changes in gravity force. 
This requires an offset from perfect balance by an amount set by scale 
factors. 
Movements are relayed to the marker 41. Such movements, however, are too 
small to be useful in most instances. They can be inspected only by means 
of a microscope directed to the marker, and this is somewhat tedious in 
that it requires continual human observation. The present invention thus 
incorporates the multiplier means which multiplies the movement by a scale 
factor to be specified. 
The first step in utilization of the device is to balance it. This requires 
movement of the weights so that the multiplier means stands vertically 
upright and true measured against the arcuate track 70 shown in FIG. 4. In 
other words, it is initially positioned in a true, upright position 
against a reference mark on the track 70. Precise centering relative to 
the chart paper is convenient, but not essential. If centered, 
fluctuations in either direction can be recorded. If not centered, the 
fluctuations in one direction may drive the graph off the paper. For this 
practical reason, an arbitrarily located initial position is determined, 
and the disk 67 is positioned in alignment with it. This is accomplished 
free of engagement with the marker 41. This requires manipulation of the 
weights which are moved to relocate the center of gravity of the 
multiplier means. When the weights have been moved to the required 
location, they are then fixed in location. At this juncture, the 
multiplier means has then been located. The carriage 74 is driven by the 
motor 78 to the beginning position where it optically detects the location 
of the target disk 67. After the marker 41 has been positioned in the 
eyelet 43, the device is then ready to operate. As gravity excursions 
occur, a mark is made on the chart recorder shown in FIG. 3. The trend of 
the marks gives gravity excursions. The line which is drawn on the chart 
as a function of time can thus be scaled to gravity variations. 
One advantage of the present apparatus is the ability to form a time base 
output on a strip chart. This compares quite favorably with other 
instruments which yield such fine movements that reading is accomplished 
through microscopes. The present invention thus has one advantage over 
other gravity meters. The present invention also utilizes a damped system. 
Damping occurs in the movement of the float 27 submerged in liquid. The 
liquid 18 determines the buoyancy, but it also serves as a damping 
material. Thus, those excursions which do occur occur with the change in 
gravity and do not include overshoot or damping oscillations. It will be 
understood that the time period of the damping system is negligible 
compared to the rate of change of gravity, and the damping, therefore, 
does not impede proper operation of the system. 
Variations can be made in the present invention. Scale factors can be 
varied as will be understood from the foregoing description. The apparatus 
is scaled to a relatively large scale which aids in reducing small, 
localized disturbances such as spot heating. Inasmuch as all the equipment 
is preferably maintained in a temperature stabilized housing with the 
temperature held over the length of the measurement to about 1.0 degree 
fluctuation, the system is quite stable. The system is also stable in that 
the equipment is constructed of nonmagnetic material. This avoids 
attraction as a result of externally created magnetic fields. This would 
be particularly undesirable if the external field were to change, and this 
is highly probable in light of the long duration of gravity measurements. 
This invention avoids that difficulty. Structural creep and fatigue are 
believed to be eliminated from this structure. The movements occur on 
knife edge bearings. The damping system is the liquid in the tank, and it, 
therefore, does not fatigue. The lack of aging, creep or fatigue reduces 
or eliminates recalibration requirements. 
The present invention incorporates a null or balanced system so that the 
weight of the equipment is not a critical factor. It is desirable only 
that the equipment be rigid and relatively strong, made of materials which 
are relatively stable and having sufficient weight which, coupled with the 
counterbalances, enables a balanced initial condition to be achieved. 
A method of operation is disclosed which incorporates the following steps. 
First of all, the tank 17 is filled with the liquid 18. The tank 27 is 
inserted into the tank 17 and is filled. The tank 27 is submerged, and oil 
is poured on the liquid 18. The oil 19 or some other liquid which has 
minimal evaporation (typically as a result of the vapor pressure of the 
liquid) is placed over the tank 27. The tank 27 is partially filled. As it 
is partially filled, its buoyancy is reduced. Filling continues until it 
is substantially brought to a nulled position. That is to say, it is 
filled to the extent that it is almost neutrally buoyant. When this 
position is achieved, the transducer of the present invention is then 
prepared. At this juncture, the horizontal beam can function as a gravity 
meter in and of itself; the difficulty with this is that indications 
resulting from its movement are difficult to obtain. Such movements are 
miniscule and, therefore, difficult to observe except through microscopes 
and other aids of this sort. 
The present invention contemplates the use of the multiplier means so 
thoroughly described above. The multiplier enhances the range of movement 
by a scale factor. The enchancement is in the range of 100 to 1,000-fold. 
Movement is multiplied by the selected scale factor. The multiplier is 
initially set in a generally upright position. Thereafter, the weights are 
adjusted to balance it so that it does not deflect to the right or left. 
This may require several attempts as fine adjustments are made. As the 
adjustments are made, the tendency to fall to the right or left is 
reduced. When the multiplier holds a steady position, then the device has 
been balanced. The linkage depicted in FIG. 5 is completed by placing the 
tab in the eyelet 43. At that juncture, a first reading can then be taken. 
The first reading will represent the reading at an initial time. This 
reading is taken and typically recorded on a strip chart. Periodic or 
timed recordings are also made over a time interval. This will typically 
show that the gravity vector is time variant. 
Through the use of two gravity meters constructed in the manner shown in 
FIG. 1, mapping can be achieved. It is not possible to make a large number 
of observations over a given geographic area at the same instant. This 
introduces time variant error in readings. These errors are removed 
through the use of two sets of equipment. For a given locale where a 
mineral deposit is to be mapped, referring to a typical gravity 
measurement procedure, the first step is to select a base station location 
and to install one gravity meter at that location. This gravity meter is 
not moved; rather, it is installed, and measurements are taken over a 
period of time sufficient to enable the gravity map to be completed. This 
may require the recordal of data over a substantial period of time. 
The second gravity meter is carried to a multitude of locations in the 
locale. Readings at each location are taken at a particular point in time. 
The relative or raw reading from each field location is temporarily 
tabulated. The reading of the base station at each particular point in 
time is also noted. The drift or deviation occurring as a result of time 
in the base station measurement is noted. This represents an error or 
offset factor. In other words, the drift of the base station from the 
beginning time (a common time for both instruments) is noted in the base 
station measurement, and the offset is added to or subtracted from the raw 
data obtained from field measurements. All field measurements are adjusted 
in this manner. If, for instance, fifteen field measurements are taken at 
one-hour intervals, then the fifteen measurements are recorded along with 
the time at which they are taken, and the adjustments to the raw data are 
thereafter made. This then brings all the measurements for a selected 
locale to a common time of occurrence. Variations which remain after this 
adjustment are indicative of anomolies in the local geology. These 
anomolies are useful in determining the nature of the geology. 
While the foregoing is directed to the preferred embodiment, the scope of 
the present invention is determined by the claims which follow.