1829.] 
Scientific Intelligence. 
309 
Mr. T. gives a very full account of comparisons made between his formula, the 
old one, and experiment- In the comparison made with Rossut’s experiments (Hy- 
drodynamkpie, Tom. ii. p. 411. or Robison's Mech. Phil. Vol. ii. p. 295) the accordance 
is truly surprising, while the difference of the old theory, from experiment, is suffi- 
cient to show that in practice it was worth nothing. Thus, when the angle with the 
direction of motion was 90°, the resistance by experiment, by the old theory, and by 
the new, is made 1000. When the angle is reduced to 0°. the resistance is by experi- 
ment 3999; by the new theory (including friction) 3578; or (excluding) 3341 ; by the 
old theory (excluding friction) 109. 
In a comparison made between the results of his formula, and the experiments 
made by Dr. Hutton on the resistance of the air, the agreement is likewise very close ; 
and still more in another series in which the body was a ball, 2 inches in diameter. 
The resistance increasing accordingto the velocity from 006 ox. to 1 700 oz. exhibits in 
but two instances, a discrepancy amounting to t’j and in one of these it is plus, in the 
other minus. And although the coincidences are not so close in some other compa- 
risons made, yet there is, upon the whole, a sufficient agreement to speak strongly for 
the practical value of the formula. 
2 .—Proposed Improvements of Daniel's Hygrometer. 
Mr. Jones, an instrument maker of London, proposed a modification of this instru- 
ment, tending to lower its price and make it more portable. It consisted in dispen- 
sing altogether with the two balls and connecting tube, while the internal thermo- 
meter, which was much enlarged, was used not only to indicate the temperature of 
the dew point, but also as the surface on which the dew should condense. It was 
in fact a thermometer with a bent stem and a large bulb, to the lower part of which, 
ether was applied, so as to diminish the temperature of the mercury ; and on the upper 
part of the bulb, which was free, the dew it was expected would deposit itself, when 
from the evaporation of the ether, the temperature should fall to that, at which the 
moisture in the air was condensible. 
The description of this instrument was honored with a niche in the Philosophical 
Transactions, an honor it was certainly not entitled to ; for Mr. Daniel having had 
such an instrument constructed by Mr. Newman, with two small thermometers 
inserted into the btdb, he found there would occasionally occur a difference of tem- 
perature amounting to 7“ between the lower part of the bulb, subject to the cooling 
influence of the ether, and the upper one left free. This was a result which every 
one must have expected, and it was confirmed by the account the purchasers of the 
instrument gave, who in fact found that no dependence whatever could be placed 
on it. 
Mr. Fogo of Leith, has recently returned to the subject, and in a late number of 
Brewster’s Journal, he recommends the simplification of the apparatus as too ex- 
pensive and bulky for the ordinary purposes of metereology. He considers the two 
balls and connect ing tube entirely superfluous, and indeed it does appear an indi- 
rect mode of proceeding to apply the cooling substance (the ether) not to the ball 
to be cooled, but to another connected with it. There iB here a double evaporation ; 
the ether evaporating from the covered ball, and from the one connected with it. This 
renders the process more tedious certainly. Mr. Fogo asks why should not the ether- 
expended on the covered ball, be used to produce a direct effect on the thermometer. 
He proposes, in fact, that a common thermometer should be used of a cylimlricalshape, 
the lower half to be enveloped in cambric muslin, confined by a fine silver wire, to pre- 
vent the spreading of the ether on the upper half, which might vitiate the experiment. 
The lower half being dipped in ether, the thermometer will begin to fall till having 
reached the temperature of the dew point, dew will be deposited on the upper half, 
which being a bright reflecting surface, will instantly show the slightest dulling. 
In the general principle, Mr. Fogo's modification is the same as that ofMr. Jones, 
and must therefore be subject to the same objection. Mr. F. notices this, but consi- 
ders the difference of size of the thermometer as a sufficient answer. There is no 
reason why the bulb should not be as small as that of Darnel's arrangenient ; and 
as in the latter, only half the. bulb is immersed, it is evident that the objection is 
equally good or bad, as made to either instrument. 
A different modification has been suggested by a Mr. Cummtng, in a late number 
of Braude’s Journal. A glass tube is proposed to be employed, open at both ends ; 
a thermometer being suspended within the tube, has its bulb surrounded with 
sponge, which is also in contact with the sides of the tube. Ether being poured on 
