Hills.] 96 [July 1, 



But if this effect of the letters, appearing in different planes with the 

 thaumatrope, is a monocular phenomenon, then we do not need Mr. 

 Claudet's explanation in reference to difference of convergence and 

 eccentric double images. I would allow that this might help to produce 

 the effect, were it not that the arc on the retina, subtended by the 

 angle between the lines from the two surfaces of card (that is, -^-^ 

 apart, and but ^-joo^ of whole distance from the eye, fifteen inches), is, 

 as I make by rough calculation, about j^^ of a millimetre, and Tobias 

 Meyer, E. H. Weber, Volkman and others, agree that two points to 

 be seen as such^ must subtend an are on the retina from -^-^^ to j-^ 

 of a millimetre. Moreover, recent experimentation has shown more 

 and more conclusively the large part accommodation takes in judging 

 of distances within its "range." When I print the alternate letters 

 of a name, for instance, L, N, O, N, on a card, and the others, I, C,L, 

 on pieces of the card, and paste them between the first, they will 

 vary in distance from my eye just the thickness of the card, in my 

 experiment -^^ inch, or -^-^ of whole distance to my eye, fifteen 

 inches. With the exception of the alternate presentation and after 

 impression, this gives me just what I have when the letters are on the 

 two sides of the card, and it is twirled by the strings. Yet placing 

 the letters as above, I get, in but a feeble degree, this effect of differ- 

 ence of plane compared with the thaumatrope experiment. I am not 

 prepared to explain to my own satisfaction this new fact of Mr. 

 Claudet, yet I desire to call attention to what seems a misinterpreta- 

 tion of its cause, as every discovery in binocular vision, now being 

 studied and experimented upon so carefully, should be thoroughly 

 tested by many observers before being admitted as a point of depart- 

 ure for further investigation. 



Mr. Luther Hills stated that he had found a new locality 

 for minerals on the Boutwell Fann, Auburn, Me., about 

 twelve miles southeast of Mt. Mica in Paris; the composi- 

 tion of the rock is the same as that of Mt. Mica. Abundance 

 of feldspar and lepidolite occurred; also graphic gi-anite, 

 rose quartz, red and black tourmaline, and gi'een tourmaline 

 of an emerald tint, differing from any found in the neighbor- 

 ing localities in Hebron and Paris. Some of these were 

 exhibited. 



