O'Eeilly — On the Barometer. 
31 
yil. — OiiT AN Optical Method by means of which the Formation op 
DEFINITE Chemical Compounds may be in ceetain cases DETERivaNED. 
Ey The Peesident. [Abstract.] 
[Read February 14, 1870.] 
This method is based upon the power which solutions of the vegetable 
alkaloids generally possess, of rotating the plane of polarization of a 
transmitted ray, and the change effected in this power when the 
alkaloid is converted into a salt. 
Applying this method to the combination of nitric acid with 
quinia, he showed that the formation of an acid nitrate (or bi-nitrate) 
was clearly indicated. 
YIII. — N'oTE ON A proposed JN'ew Method of disposing the Baeometeic 
Column so as to fuenish dieectly enlaeged Indications, without 
THE INTEEMEDIAEY OF A SySTEM OF TeANSMISSION OF MOVEMENT. By 
J". P. O'Eeilly, Esq., Professor of Mining and Mineralogy, Eoyal 
College of Science. (Plate XI,) 
[Read February 28, 1870.] 
Having been led to examine the question of the arrangement of a ba- 
rometric column capable of rendering clearly perceptible minute varia- 
tions of the mercury, I was led to imagine, and have had carried into 
execution, the plan which I beg leave to submit to the Academy, 
and which I purpose to explain in the following note. 
The ordinary barometric column undergoes in our latitudes an ex- 
treme oscillation of about Ij inches, and consequently small variations 
cannot be rendered clearly perceptible to the eye, however accurately 
they may be measured by the instrument. 
On the other hand, the wheel barometer, so ordinarily in use for 
observations in connexion with changes of weather, is defective, by 
reason of the system of transmission employed for communicating the 
vertical movements of oscillation of the mercury to the dial index ; its 
indications have, however, the advantage of being very perceptible, 
and, so far, have a special utility. The problem which I considered 
was, the combination of the exactitude of the vertical column with the 
distinctness of indication of the wheel barometer, without the interven- 
tion of any system of transmission. 
My first idea was the establishment of the column in an inclined 
position, so that the mercury, tending to rise or fall through a certain 
vertical distance, in consequence of a change of pressure, should be 
obliged to traverse a length of inclined tube proportional to its inclina- 
tion from the vertical. In this manner the extreme length of oscil- 
lation of the mercury might be doubled, at least, and consequently 
more minute variations rendered observable. Subsequently, on exa- 
