CONTENTS. 
I. On the effects of temperature on the intensity of magfietic forces ; 
and on the diurnal variation of the terrestrial magnetic inten- 
sity. By Samuel Hunter Christie, Esq. M. A. of Trinity 
College., Cambridge, Fellow of the Cambridge Philosophical 
Society : of the Royal Military Academy. Communicated by 
the President p. i 
II. The Croo?iia?i Lecture. On the existence of Nerves in the 
Placenta. By Sir Everard Home, Bart. V. P. R. S. 66 
III. Observations on the changes the Ovum of the Frog undergoes 
during the formation of the Tadpole. By Sir Everard Home, 
Bart, V. P. R. S. 
8i 
IV. A general Method of Calculating the Angles made by a?iy 
Planes of Crystals, and the Laws according to which they are 
formed. By the Rev. W. Whewell, F. R, S. Fellow of 
Trinity College, Cambridge. 87 
V. Explanation of an optical deception in the appearance of 
the spokes of a wheel seen through vertical apertures. By 
P. M. Roget, M. D. F. R. S. 131 
VI. On a new photometer, with its application to determine the 
relative intensities of artificial light, &c. By "William 
Ritchie, A. M. Rector of the Academy at Tain. Communicated 
by the President, 141 
VII. The description of a floating Collimator, By Captain Henry 
Kater, F. R. S. 14Y 
