462 Analyses of Books. [Dec* 



whatever eflfects are produced may easily be observed with con- 

 siderable precision, the time required for each observation being 

 not more than five minutes ; another is, that, the magnets being 

 immersed in water, as far as regards them, we may command 

 the temperature at which the observations are to be made, and 

 thus limit the correction for temperature to a very small quan- 

 tity ; and it possesses another decided advantage, that whatever 

 are the effects produced on the needle by atmospheric changes, 

 they are, by means of it, rendered immediately visible, and can 

 be observed as they occur." 



II. The Croonian Lecture, On the Existence of Nerves in the 

 Placenta. By Sir E. Home, Bart. VPRS. (See Annals for 

 January last.) 



III. Observations on the Changes the Ovum of the Frog under- 

 goes during the Formation of the Tadpole. By the same Author. 



" In the year 1822,'' Sir Everard observes, '* i laid before the 

 Society a series of observations on the progress of the formation 

 of the chick in the egg of the pullet, illustrated by drawings 

 from the pencil of Mr. Bauer, showing that in the ova of hot- 

 blooded animals, the first parts formed are the brain and spinal 

 marrow. I have now brought forward a similar series on the 

 progress of organization in the ova of cold-blooded animals, 

 illustrated in the same manner by microscopical drawings made 

 by the same hand." 



By comparing together the first rudiments of organization 

 in the ova of these very distinct classes of animals, he shows 

 that in both the same general principle is employed in the 

 formation of the embryo, although the respective ova are 

 not composed of similar parts. Those of the frog, which have 

 been selected for this investigation, being found to have no 

 yelk. 



IV. A general Method of calculating the Angles made bt/ any 

 Planes of Crystals^ and the Laws according to which they are 



formed. By the Rev. W. Whewell, FRS. Fellow of Trinity 

 College, Cambridge. 



*' It has been usual," Mr. Whewell states in the commence- 

 ment of this paper, " to calculate the angles of crystals and 

 their la^s of decrement from one another, by methods which 

 were different as the figure was difterently related to its nucleus; 

 which were consequently incapable of any general expression or 

 investigation, and which had no connexion with the notation by 

 which the planes of the crystals were sometimes expressed. 

 And the notation which has hitherto been employed, besides 

 being merely a mode of registering the laws of decrement, 

 without leading to any consequences, is in itself very inelegant 

 and imperfect. The different modes of decrement are expressed 

 by means of different arbitrary symbols ; and these are combined 

 in a manner which in some cases, as for instance in that of inter- 



