374 
of the earth’s crust, and whose diameter is one foot. Even 
with a fluid nucleus exercising so powerful a friction as this, he 
finds that for a thickness of shell = 20 miles, the increase in 
the length of the day in 3000 years would be less than 
O”.O1. 
In fact, the increment would be much less than this; for this 
calculation is made upon the supposition, that the separation 
between the arcs has at all times its maximum value; and 
that this value is that which it would have if no friction ex- 
isted. The real separation, is, of course, much less than this. 
If the crust of the earth had a thickness of 1000 miles, the 
increment would probably be less than 
9” .00O1. 
For a particular thickness of crust, determined by Mr. 
Hopkins to be about 800 miles, the foregoing reasoning ceases 
to be applicable, and the separation might attain a much 
greater value; but, with our present imperfect knowledge of 
the laws of motion of viscous fluids, it seems impossible to 
give a complete solution of the question. 
Mr. Hennessy, the Rev. Samuel Haughton, and Mr. Jukes, 
made some remarks on Mr. Jellett’s Paper. 
The President called the attention of the Academy to the 
fact that the Council had authorized the late President, Rev. 
Dr. Robinson, and the Rev. Dr. Lloyd, on their part, to jom 
the University of Dublin, and other institutions in this city, 
in an invitation to the British Association for the Advancement 
of Science, to hold their annual meeting for 1857 in Dublin; 
whereupon— 
Iv was RESOLVED,—That the Academy do highly approve 
of the action of the Council in this matter, and request the 
President to convey to the permanent officers of the British 
Association their complete concurrence in the invitation. 
