New-York tribune. [volume] (New York [N.Y.]) 1866-1924, 1875-07-26
APPLIED. SCIENCE.

FRENCH METHOD IN ENGRAVING ON wooD.-A
French method in engraving wood consists in nrst
covering the block with layer of gelatin SO.3e
prams to 81 grams of water by means OF soft
brush When this coating is dry is covered. in the
dark with solution prepared Of o. red prus
siate of potash $50 grams water. 22O grams; SZ)
ammonia citrate of iron, 910 grams in S2 20 grams
water. These solutions are mixed and uttered, anu
dry II is EXPOSED under a negative from 10 to IL
minutes, and washed with soft sponge, when t u
blue image appears. II thus prepared the coatihg
does not Shell off under the graver.
A VERY DELICATE BARoMETER.-An ingenious
device has been constructed by Mendeief, which
shows the slightest variations of pressure by means
of a small U-shaped tube containing petroleum
oil One end of this tube is closed, and contains
certain volume of dry air maintained at constant
temperature while the other end is open to the ar
Tho instrument being accurately adjusted by means
NJ merourial plunger connected with the bottom OF
the U-shaped tube so that the petroleum IL exaoS
IN level in the branches of the tube IL is iouu
70 he so extremely sensitive that the slightest yafia
fon of atmospheric pressure is shown by the atera
tion of the level, aud the amount OF TINS aiteIauoh
can be measured with the greatest precision
THr DEPOSITION OF FINE SEDIMENTs.-Dr. L.
Sterry Hunt states in reference TO the quesuoh oi
the deposition of fine mud in the MISSISSIPPI,
that thc deposited matter requires from 10 to IA
pburc acid be added to the turbid water it becomes
clear in from IL to 1s hours. Thus is explained the
rand precipitation that when the river water
MIXES with the salt waters of the Gulf OF Mexico.
The cohesion of water diminshes when II holds
saline matter in solntion as was SAID by .uthrie an
was verified by DIR. Hunt lie found that the audi-
tion of parts of chloride OF calcium 10 lvov par.
If water reduces tie size Of drops TO one-Iinth and
the precipitation OF suspended cray Is i i, ~
rapid when q strong solution OF salt Is ehipio!eu
THE CONSTRUCTION OF WINDING STAi.CAsLs'
In Major ElliJtt's Report on European Lighthouses
he notes that in several cases the STAIRS are CIRCULAR
and apparently self-supportng, one end only ocihe
built into the wall, as in the Treasury at Washing
ton This method of stair-building is, he observes,
universal in Europe, both in private and pubic
buildings The most recent lighthouse towers oil the
American system are constructed with conicai In
terior walls aud iron starcases winding around the
interior of the European towers are sen"raiY
constructed with exterior ccmcai ana an Interior
cylindrical wall leaving an unnecessarily large IN
used space between the two The amcnn OF ihaSonr!
m the American system is the same as IN the Luro-
pean and is better calculated 10 resist the o'ctuih
ing effect of the seyercst gales
STEAM Foe WHIsTEs.-It has been found
bv Gen. Duane of tho United States Ehsl-
neers. in his experiments made to determine
the best form of boilers for steam fog Signals
that as the steam used is at high pressure and is
IN foam and throw out water with the steam. 10
counteract this a horizontal tubular boiler hike
tbose need in locomotives. is recommended by HIM:
The stea m dome must be very large and slnOuuted
lv steam pipe II inches III diameter. Inc steam
s6onld be drawn off at point ten feet above the
wafer level in the boiler. The diameter OF The boiler
whistle should be two-hirds OF ITS L.nsth ana inc
vertical dstnoe Of its lower edge above me coping
for n steam pressure of 80 pounds should be from
,ne-tbird 10 one-fOurth of the diameter.
AUTOMATIC REGISTRATION OF THE CHEMICAL
Action OF LlGHT.-The measurement of the cheini-
cal intensity of the solar light has not yet become
subject of regular meteorological observation, be-
couse of the want Of a proper instrument. his
want is now partly supplied by method proposed
by Roscoe, who proposes 10 effect the measurement
by the backcning Of paper saturated with chloride
of silver or rather by means OF the time required Ill
order that the exposure to the light may bring about
the given intensity of shade. uniformly prepared
paper is placed in the apparatus during the previous
night. and is, by mechanical arrangement, hourly
exposed duripr given interval to the sunlight. In
order 10 estimate correctly the intensity of the solar
action, Roscoe aIranges the apparatus so tnae IN"
naner shall each hour. many times III quick success
sion from two to thirty seconds, be exposed 10 the
LIGHT We thus have at each hour OF The day, q
complete series of small spots OF various tints ana
have only seek that tint which corresponds to the
normal 10 know at once the number OF seconds OF
exposure corresponding 10 the sreneth on me sun
Tcht al that time. A series Of observations made
during the months OF May, June, ana JAY, nave
given very aecorant results III the hands OF Roscoe
ADVANCES IN PHOToGRAPDY.-ln review OF re-
cent discoveries in photography Medola states that
since the wear 1912, when Becquerel photographed
the whole solar spectrum and DR.. Draper the violet
blue. and ultra red, successful attempts have
been made to photograph the red end OF the spec
tr,,m Becuuerels result was obtained by film of
silver iodide first exposed to ditfused light, and then
10 the action of the spectrum, by which processes he
was able to photograph the entire spectrum from the
ultra violet to the ultra red. During the past year
DIR. Vogcl has demonstrated that by vanishing
the ordinary bromide Of silver plates with
dive of coralline, we get the maXlmum OF
Photographic action in the indigo and the yellow
and by using aniline green the maximum Of activity
i'm the indigo and red. Again, Becquerel has dls-
solved coralline in the Odized coodion film aud
ATTAINED similar results. The most remarkable ac-
ton was observed in the case of cblorophyl by the
use of which spectrum image of great length was
obtained from the ultra violet 10 the green with
weaker impression from the green 10 the red. Con-
Thinning these observations IN connection with what
has more recently been published by Loekyer, we
find every reason TO announce, as probable iaV
that the optical observation OF the bands OF any
chemical show the active rays for that chemical;
and that, therefore, by proper selection OF dyes,
sensitive plate may be prepared especially adapted
To any to all operations on the spectrum
New PnoToMETERs.-M Elliot reports that in
his visit 80 the establishment of Messrs. Chance at
Birmingham the scientific director in charge Dr.
Hopknson, presented him with photometer OF his
own invention for the comparison of lights at dis
lance 1t is very compact and consists OF two Nlco
prisms which can be moved relatively to each other
in azimuth. A little tube carries the analyzing
prism and second tube contains the poar:zing
prsrn The latter being turned until the observed
light is Just diminished TO the point of inyisbity,
and another light being then observed in the same
a., 10 4l.av