Evening star., 1897-03-06

ber of viru!ent microbes lodged In the hu-
man body will cause a mans death ana
yet. according to a recent computation. q
cubic ceutiueter OF water may contain
not millions but billions of these deadly
parasites Recently the milk supply of
Boston on examination. yielded as Efgh
as 1S5.Oa0.ao germs psr ounce 1t Is as
tions are made rapidly. and that COM
putation reaching even into the biiIlons
may consume only a minute or so. MS
is done by means of extremely fine rulings
or lines in the field of the microscopic
vision and the simple process OF counting
the number of microbes in one OF these
squares and multiplying ous this sum yleios
the desired knowledge
Then again. in making high power MI
croscopes the lenses are. to all intents and
purposes. flat: that is. no ordinary eye
could detect their curvature, which Is OFTEN
10 more than LILO GOOth of an inch In
order to iiquefy air Professor Dewar of
London desired to attain the nearest ap-
p-oximation to perfect vacuum. AR
has a pressure OF fifteen pounds to the
square inch, and this Is called an at'nos-
phere in technical language We DO not
feel this pressure ordinarily. but Professor
Dewar succeeded In gaining vacuum Vi
1-25 ot0 0spth of an atmosphere by nihhs
a vessel with mercurial vapor ana eA-
posing IL to a very low temperature.
human being would die in an atmosphere
rarified two-thrds. but Professor Dewar
goes a little farther To be exact 10
where his air is rarified to 1-2.3OO.Up,WOtn
of its original density
Next as regards angles 1t Wouid De
unite trnpossible to detect with the eye
penny at distance of 1.WO feet snppoS-
ing II were 1.U1 miles away, the angie
formed by its diameter at this distance
would be so incredibly small that we nave
no means of pcturing 1t to ourselves but
the Darwin pendulum will Indicate move
ment of Sfstth of a second. whfcn Is just
about the angular measlirement OF penny
at this distance OF i,opp miles,
prof IangIey's bolometer measures the
temperature of the sun. though that oro
ia ?; ODoO00 miles away. A galvanometer
has heeu devised sensitive that IL VIII
chow the electric current set up by the dl1-
ference in temperature between TWO coh-
tieuous fingers of your hand. even II
very good thermometer shows no ciHer-
erce OF warmth whatever. one per cent
OF arsenic In copper does not seem Srede
deal but il there be but three one-thou-
sanlthS of per cent in copper ware,
In is unfit for use electrically. Chemical
ANALYSIS in every day use detects THIS OH
ference and even very small fractions OF
such difference. 1t is not at all an unusual
thing to solution marked as contain
ing Osspp1 of gram. and an ordinary as
say balance works down TO ore one-huIi-
drcdth OF a miligram- A diamond Weighing
a carat is not an extraoTd Tdnary affair. but
this same balance will weigh down to one
one-thousandth of this
Delicate Instrument.
One OF the most exquisitely sensitive in
etruments ever devised has just been set
UP by Gus Henning, mechanical engi-
neer of New York. who has constructed
some of the finest instruments Of measure
ment in the world. This is known as the
mirror-testing apparatus. and is designed
to test and register the expansion or
stretching of metals under heat or strain.
Seen in the compact little box in which 1t
is carried one would never dream that this
I'll.
measuring the strain caused by the foot
fall of a pedestrian crossing Brooklyn
bridge. And yet such is its power.
This instrument is exceedingly simple. Its
chief parts consists OF a ccrple OF little mir
TCrs carried Oh spindles. which. in turn. are
fastened TO a pair of knife edges that
the slightest change in the position of the
knife edge causes detection of the mir
rOrs- For the rest there is ordinary
reaGirg telescope. to which Is attached
finely graduated scale I<0Aing down 10
1-lDp.0oDth OF AN inch. These readings can
rot. of course, be detected with the naked
eye. but only through strong telescope.
Now. wh-r the knife edges are lightly
clamped against the object to be tested
say bar Of steel. and the latter be
stretched or expanded. the knife edge will
change POSITION. the mirror will be de-
Elected and as the latter Is looked at
through the telescope from a distance of
five or ten feet. the graduated scale which
the mirror reflects seems to move up and
down And by watching these movements
the stress on the bar is easily calculated
1t goes almost without the telling that
An instrument sensitive as this and
dealing with graduations OF 1-10O.OOot
part Of an inch. will register the most
minute changes of temperature. The mere
proximity of the body will. by the expan-
sion due to the heat radiated therefrom
introduce errors. and in fact the utmost
precaution must be taken IN this regard to
see that the temperature OF the room in
which the Observations are TO be made
does lot vary while they are In progress
moreover. nervous or excitable persons
cani-ot use such delicate micrometers at
all. and even for others considerable ex-
pertence Is necessary before one can be-
come expert in their use and their delicate
readings be of practical value
This Instrument is very much more ac-
curate than another remarkable microm-
eter devised by Mr.. Henniny for the same
purpose. known as toe duplex measuring
instrument In the latter dsvice the ex-
pansion or compression Of the piece TO be
tested was made to affect the closure of an
electrical circuit wnich rang a bell when
the contact was made. Manipulation OF
screws gave the |iesired~ reading. which
were down TO 1-10.OOOths part of an inch
This was wonderful enough in Its way
but the new apparatus Is so much more
delicate that with snfil Sieutly strong
telescope placed about twenty-five fee,
away 1t would be possible TO read down tc