GENERAL MEETING. DY 
restrial magnetism is eliminated. The force produced by the current 
is opposed by a weight and is thus measured in terms of gravity. 
Mr. MENDENHALL also renewed the discussion of the preceding 
evening on reaction time, reciting the methods and results of his 
own experiments in 1871. 
Remarks on the volt-meter were made by Mr. Ev.tiort, on re- 
action time by Messrs. Pau, Mason, and MatTHews. 
Mr. Wiii1Am HarxkNness made a communication on 
FLEXURES OF TRANSIT INSTRUMENTS, 
pointing out that the flexures induced by the weight of a transit, in 
positions other than vertical, are not eliminated by reversing the 
instrument, and developing equations for the discussion of the errors 
so far as they can be determined by the aid of collimators. 
\ 
275TH MEETING. NovEMBER 7, 1885. 
The President in the Chair. 
Sixty-nine members present. 
Mr. F. W. Ciarke made a communication on 
AN ATTEMPT AT A THEORY OF ODOR, 
in which he accounted for the lack of knowledge as to the con- 
ditions of action of this sense by the difficulty of dissociating it from 
taste; and, while disclaiming any thought of attempting a physio- 
logical explanation of the sense, proposed the following as the essen- 
tial objective conditions : 
1. To be odorous, a substance must be volatile, so that it may 
come into contact with the mucous tissue of the nose, and 
2. It must be chemically unstable, so that it may undergo chemi- 
cal changes in contact with that tissue. 
Mr. Clarke gave some confirmatory instances, from the compounds 
of hydrogen with sulphur, selenium, and tellurium, and from the 
C, H,, O, group of acids (formic, acetic, etc.) 
Mr. ANTISELL called attention to the connection between a low 
boiling-point and simplicity of chemical constitution, and to the 
associated fact that organic substances containing a large number 
