388 
JUNE 23RD, 1856. 
JAMES HENTHORN TODD, D.D., Presipent, 
in the Chair. 
Ropert Patrerson, Ese., was elected a Member of the 
Academy. 
The President exhibited the original Captain’s commis- 
sion, granted in the reign of James II. to the great-grandfather 
of Michael Warren, Esq. 
Professor Hennessy read a Paper on the influence of the 
earth’s internal structure on the length of the day. 
Having stated that changes in the distribution of the mat- 
ter composing the interior of the earth will generally tend to 
alter its velocity of rotation, and thus vary the length of the 
day, the author proceeded to examine the probable nature of 
such changes. Laplace had already examined the effect of 
the cubical contraction of the globe considered as a cooling 
solid’;* but if the earth consists of a solid shell filled with 
matter in a state of fluidity, the inquiry assumes a different 
shape. Hitherto this, as well as all other questions con- 
nected with the general structure and rotation of the earth, 
had been treated on the assumption that the particles of the 
fluid underwent no changes in their positions on assuming the 
solid state. In his ‘Researches in Terrestrial Physics,” Mr. 
Hennessy had pointed out the necessity of abandoning this 
assumption, and he, moreover, investigated what would be 
the internal structure of the earth on the supposition that it 
consists of matter possessing a recognised property of the 
igneous rocks at its surface—namely, of contracting in volume 
* Mecanique Celeste, Livre XL. + Philosophical Transactions, 1851, Part IT. 
