28 
From these results we learn that— 
1. The effect of a distant magnetic body consists of two parts, one 
of which is constant throughout the day, while the other varies with the 
hour-angle of the luminary. 
2. Each of these parts varies inversely as the cube of the distance of 
the luminary. 
3. The variable part will give rise to a diurnal inequality, having 
one maximum and one minimum in the day, and subject to the condi- 
tion— 
Ag + Az.o= 0. 
This law does not hold with respect either to the solar or to the lunar 
diurnal variation. 
Thus, in the solar diurnal variation of the declination, the changes 
of position of the magnet throughout the night are comparatively small, 
and do not correspond (as required by the foregoing law) to those which 
take place at the homonymous hours of the day. The phenomena of the 
lunar diurnal variation are even more opposed to the deduced law, the 
variation having two maxima and two minima, of nearly equal magni- 
tude, in the twenty-four lunar hours, and its values at homonymous 
hours having, for the most part, the same sign. Hence the phenomena 
of the diurnal variation are not caused by the direct magnetic action of 
the sun and moon. 
Mr. Henry Conybeare communicated a short notice of the works 
recently erected for the purpose of supplying the city of Bombay with 
water. 
It was stated by Dr. Stokes that Mr. Groux, a gentleman haying 
congenital fissure of the sternum, was at present in Dublin, and that 
the Academy would confer a great benefit on medical and anatomical 
science if they would appoint a commission to inquire into his case. It 
was then resolved that the Council be requested to consider the propriety 
of appointing a commission to examine and report on the case of Mr. 
Groux. 
The Secretary announced the presentation by her Majesty’s Govern- 
ment of a collection of 514 volumes of Statutes, Journals of the Houses 
of Parliament, London Gazettes, and Newspapers, as a donation to the 
Library of the Academy. 
Resolved,—That the thanks of the Academy be presented to Colonel _ 
Larcom, by whom this large donation to the Library has been made to the 
Academy. 
