New-York tribune. [volume] (New York [N.Y.]) 1866-1924, 1874-10-08
APPLIED SCIENCE.

DIFFERENCE OF TEMPERATURE BETWEEN THE
Country AND Cry. This difference has been
investigated by Fines who finds that, as has been
also generally ascertaned by other observations,
the mean annual temperature in the interior OF q
city Is decidedly higher than outside. On the other
hand the maximum temperatures in the Fan and
Winter somewhat lower in the city, while In the
Spring and Summer they are somewhat higher On
clear nights the difference between the minimum
temperatures in the city and the country may
amount to 1879 Fab, that in the country being the
lower of the two. Also, the annual average Differ
ence between the maxima and the minima is greater
for the country than the city.
OBJECT GLASSES FOR PHoroGRAPHY.-In a paper
on the transformation of the optical achromasm OF
an object glass into chemical achromatism, Cornu
finds that given an achromatic telescope the object
glass of which is formed of cOnvergent lens OF
ground glass and divergent lens of flint glass, this
object glass may be formed into capable OF giving
satisfactorily distinct Photographic images, by
separating the two lenses to extent dependent on
the nature OF the two glasses-a method which, by
the by, was 6rst introduced by Rutherfurd in 1880
but subsequently abandoned by him for better.
With the glasses used in optics a separation OF Ii
per cent of the focal distance of the object glass is
sufficient and the chemical focus is then very near
the optic focus. Using an excellent telescope OF
about four feet focal length, and separating the OBJ
jet glasses BY 90 Of inch. be succeeded in photo
graphing divided scale placed at over lou feet dis
lance; the lines were quite distinct.
The EFFECT OF LIGHTNING ON TREEs.-The
theory that the splitting of the trunks of trees by
lightning is the result of the sudden evaporation OF
the liquids contained within them has received
much confirmation from experiments made by Osborn
Reynolds, who succeeded in splitting small sticks of
wood by passing the electric spark through them
after they had been impregnated with water He
also burst small glass tubes, which were filled with
water, although the tubes, when empty,
allowed the electric spark to jump through them
without in the least disturbing them. The most
striking experiment made by him upon a tube
three-eighths of an inch exterior and One-eighth
interior diameter which could stand pressure OF at
least 200 atmOspheres to the square inch; this tube
was Il inches long and bent at a right angle.
very large electric flash being sent through the tube
it was split by the first discharge. and the pieces
thrown to distance of several feet. The inner sur
face of the tube was, in fac completely pniverzed
as though it had been struck by hammer. Reynolds
estimates that the pressure must have been more
than 600 atmospheres.
MEASUREMENT OF GALvANIc CURRENTS. Mr..
Latimer Clark states, in reference to common
source of error in the measurement Of currents of
short duration, that when using galvanometers with
stunts certain discrepancy has been noticed, which
bration of the needle of the galvanometer and on
endeavoring to ascertain the of this discrep
ancy he discovered that the results given by the
use Of resistance coils correct, and that those
obtained by the of cOndensers were wrong. The
cause of the error he traces up to the fact that
the movement of magnetic needle tends to in
duce in the coil within which it is sus
pended, a current in the opposite direction to
that producing its DETECTION. A larger proper
ton of the whole current consequently passes
by the sbunt, which is not subject to the influence
of the needle. If, therefore, two galvanOmeters are
used, the movements of the needles within their
coils being similar. each of them counteracts the
Others influence thus cOncealing the of the
process. This source of error does not exist when
the is made by differential galvanOmeter.
DE Sauty's method OF comparing measures Is also
free from this of and, in general, he
concludes that il is better in testing submarine ca
bles, to avoid the of c0ndensers for comparing
batteries with standard cells and to make use rather
of very high resistance coils; and he has generally
recommended the use OF a resistance as high as
10000 ohms.
THE DIsAGGREG ALTON OF TIN.-One of our for
egn contemporaries records as a great rarity curl
GUS case of the dsaggegatOn Tor disintegratiOn of
metallic tin. The facts of the follows:
commercial house at Rotterdam had dispatched a
quantity of tin in form of pigs bv railway, during
hard FROST II arrived at its destination powder
composed of large crystalline grains. Its appear
ance was unlike that of tin of good quality, that
an examination of its composition was undertaken,
which resulted in showing that it almost abso-
utey pure tin contrasting less than three per cent
of foreign substances lead and lron). 1t
was found to be impossible to reunite by flu
SION the metal so curiously divided, for
in the attempt it gave rise to such
quantity of oxide Of tip that t1e product was
nothing better than Rray powder. The explana'
ton offered to account for this case is that the dis
aggregation of the metal tie result of the COM
bned influences of cold and vibration. 1t should,
However. be said that the phenomenon Is by no
means an exceptional isolated One several anaio-
gous cases having been quite recently reported. The
Exclamation above suggested seems, In the absence
~ thorough investigation to be at least reason
able and places the case IN the same category with
the molecular changes which are frequently known
TO occur with other metals when exposed to long
continued vibration.
PREPARATION OF PHoToGRAPHIC DRY PLATES BY
DAYIIGHT.-The following process suggested by
Prof Hines, for the preparation of Photographic
dry plates, renders unnecessary the prolonged. I'M
pleasant, and unhealthy confinement TO the damp,
dark room, and in great measure lessons the iabll-
ity 70 accidental stains the plates. 1t rests upon
the fact ascertained by him. that at least any effect
capable of development, of light upon iodide or
bromide of silver may be removed and further ac-
ton of light prevented. by the application of solu
ton of odide of potassium of similar substances
or even by prolonged action of sunlight alone but
that these silver salts may again be rendered sens
tive to light by treating them with solution of
tannn or of nitrate of silver, or by exposing them
TO fumes of ammonia. Glass plates, therefore,
coated with the usual bromO-iodized colodion. are
plunged in the nitrate of silver bath in ordinary
wel-lighted room; the of nitrate of silver is
rinsed of with water and solution of about FIVE per
cent of iodidc of potassium is allowed to flow over