537 



the same cellars, three weeks later. The tadpoles were of a large 

 size. I obtained the same result, the full development of the 

 frog in the absence of light ; but in this experiment I had another 

 object in view, that of observing the growth and obtaining the exact 

 weight of the tadpoles before, during, and after their metamorphosis 

 into a frog. 



Dr. Edwards said that in his experiment " the tadpoles attained an 

 extraordinary size, doubling or trebling their usual full weight ;" but 

 he unfortunately does not mention any particular weight, or how long 

 the tadpoles were preserved alive ; in fact there is nothing definite. 



During my several years of experiments I did not observe any re- 

 markable increase of weight or size as mentioned by Dr. Edwards, 

 although my first experiment was from the ovum to the full develop- 

 ment of the frog, and the two last when the tadpoles were approach- 

 ing the period of their development. 



In my first experiment on the ovum, I never obtained a tadpole 

 more than 8 grains in weight in the absence of light ; but I found 

 in a pool in the neighbourhood a number of tadpoles, some between 

 11 and 15 grains in weight ; seven of them weighed 15 grains each. 

 Of these large tadpoles I took twenty for my experiment, weighing 

 altogether 264 grains, and averaging about 13 grains each. After 

 their transformation the frogs weighed 93 grains, averaging about 4| 

 grains each, those of 1 5 grains in the tadpole state only weighing 

 5 grains as frogs, having lost two- thirds of their weight during their 

 metamorphosis. 



Subsequent experiments have been in accordance with the above. 



III. "Note on Internal Radiation." By GEORGE G. STOKES, 

 M.A., Sec. U.S., Lucasian Professor of Mathematics in the 

 University of Cambridge. Received December 28, 1861. 



In the eleventh volume of the 'Proceedings of the Royal Society,' 

 p. 1 93, is the abstract of a paper by Mr. Balfour Stewart, in which he 

 deduces an expression for the internal radiation in any direction within 

 a uniaxal crystal from an equation between the radiations incident 

 upon and emerging from a unit of area of a plane surface, having an 

 arbitrary direction, by which the crystal is supposed to be bounded. 

 With reference to this determination he remarks (p. 196), "But the 



