REPORT ON METEOROLOGY. 
227 
tiful modification of this plan has been invented and adopted by 
Dr. Prout in his admirable standard barometer, one of the finest 
philosophical instruments I ever had the pleasure of seeing ; by 
means of which he informs me he can ascertain the lower level 
of the mercury to much greater precision than he can read off 
upon the scale, which is divided to single thousandths of an 
inch. As no account of it has been published, it would perhaps 
be out of place to give any description of it here. 
Dr. Jacob proposed a cistern in which the mercury assumed 
a constant level by merely being permitted to overflow Mr. 
John Adie of Edinburgh has contrived a mode of adjusting 
the level of the mercury without a leather bag, which in great 
hygrometric extremes may become unmanageable “f, by substi¬ 
tuting a glass plunger with a stuffing-box J. 
The difficulties arising from want of portability, have some¬ 
times brought the instrument back to its earliest stages of sim¬ 
plicity. Some observers now strenuously recommend the prac¬ 
tice of constructing a temporary barometer at the place of 
observation, by filling a tube with mercury, thus dispensing 
with the precaution of boiling. A distinguished Russian 
philosopher, M. Kupffer, recommends that air he left above 
the mercury , and its effect computed §. Neither of these 
plans can we approve, more especially the latter, as the effect 
of temperature, the difficulty of ascertaining which we have 
already noticed, becomes tenfold more important. Upon the 
whole we cannot flatter ourselves that the barometer as an in¬ 
strument has made much progress towards perfection for some 
time past. In stationary instruments simplicity and solidity are 
important requisites; and there is one interesting fact which, 
though frequently suspected, can hardly be said to have been 
substantiated till lately by the observations of Mr. Hudson, the 
indefatigable observer to the Royal Society of London,—that the 
sensibility of barometers depends much upon the bore of the 
tube, which he has found to have a sensible effect even when it 
is by no means small ||. 
The manometer of Hooke was revived about twelve years 
ago by Mr. Adie of Edinburgh, under the name of the Sympieso- 
meter, and he has conferred upon it the most essential im¬ 
provements and the means of giving indications of very con- 
* Dublin Philosophical Journal, No. IV. 
f As Captain Hall found near the cataract of Niagara. 
X Edinburgh Journal of Science , N.S. i. 338. 
§ St. Petersburgh Transactions, 1830; and Journal of the Royal Institution, 
N.S. vol. i. 
|| Published (since the above was written) in the Philosophical Transactions 
for 1832, Part II. 
p 2 
