96 
PROCEEDINGS OF SOCIETIES. 
months; and perhaps not the least interesting would he to ascertain 
whether they, like the gregarious summer visitants, return to their old 
localities or not. 
Mr. Grubb exhibited a microscope of his own construction, which 
combined a steady stage, the power of placing the tube in either a ver¬ 
tical or horizontal position, and of applying every kind of illumination 
seriatim, without taking the eye off the object. He entered fully into 
the history of the improvements introduced in illuminators as regarded 
illumination, and the azimuth as regards the object, explaining the 
nature of Shadbolt’s illuminator, as modified by Mr. F. Bergin, the 
objections to the method, and his own improvement of a mirror revolv¬ 
ing on an arc. 
Mr. Grubb explained and exhibited to the Meeting a series of beau¬ 
tiful manipulations illustrative of the improvements in the microscope 
he had made. 
After the ballot, the Chairman declared Henry P. Heney, Esq., duly 
elected Ordinary Member. 
The Meeting adjourned to the first Friday in March. 
BOYAL I El SH ACADEMY. 
MONDAY, JANUARY 11, 1858. 
Humphrey Lloyd, D.D., Yice-President, in the Chair. 
Alexander T. Blakeley, Esq.; Maurice Henry Collis, M.B.; Howard 
B. Montgomery, M.D.; and John Purser, Jun., Esq.; were elected 
Members of the Academy. 
The Eev. Dr. Lloyd read a paper—. 
on the determination of the intensity of the earth’s magnetic 
FORCE IN ABSOLUTE MEASURE, BY MEANS OF THE DIP CIRCLE. 
The received method of determining the intensity of the earth’s mag¬ 
netic force is unsuited to the high magnetic latitudes, the error of the 
deduced force, arising from a given error of inclination, becoming very 
considerable when the latter approaches to 90°. To remedy this defect 
the author suggested, some years since,* another process, in which the 
total intensity is found directly by means of the dip circle,—the pro* 
duct of the earth’s magnetic force into the magnetic moment of the 
magnet being determined by the position of equilibrium of the dipping- 
needle, when loaded with a small weight, and the ratio of the same 
quantities being found by removing the needle, and employing it to 
See “ Proceedings,” January 24, 1848, 
