218 = 
sound, viz. that its intensity is measured by the amplitude or 
the square of the amplitude of the vibrations by which it is 
produced, which he considered incomplete when waves of dif- 
ferent lengths are compared. The conclusion at which he 
arrived was that, if two notes were sounded separately, differing 
by seven octaves, when the tympanal cavity was exhausted or 
inflated, the force of resistance to the motion of the aural nerve 
was the same in either case, but that the primary force (that 
which is lessened by the resistance) was 128 times as great in 
the one case as in the other; therefore the resistance in the 
one case might be sufficient to stop the motion of the nerve 
entirely, i.e. to suppress the note, while in the case of the higher 
note, the effect on the motion of the nerve, and therefore in the 
degree of distinctness with which the note is perceived, might 
be practically inappreciable. 
May 1, 1871. 
The PRESIDENT (PROFESSOR CAYLEY) in the Chair. 
New Fellows elected : 
Rev. G. HALE, M.A., Sidney Sussex College. 
Rev. C. Smiru, B.A., Sidney Sussex College. 
A. G. GREENHILL, B.A., St John’s College.' 
Communications made to the Society : 
On the Measurements of an Arc of the Meridian in Lap- 
land. By I. Topuuntsr, M.A. 
The object of this Memoir was to draw attention to the numer- 
ous errors which have been made, even by distinguished astro- 
nomers, in their accounts of the two measurements of an arc of 
the meridian in Lapland. A comparison of the original autho- 
rities on the subject at once detects these errors and aes 
the necessary corrections. 
