248 THE CANADIAN NATURALIST. fJune 



expanded ends. Another form shows a curious dice-box, resulting 

 from a bundle of such crystals. Probably they are some silicate 

 of soda, modified by the presence of other bases. 



Columbic acid is deposited from borax in crystals which often 

 have similar forms ; whereas titanic acid gives hair-like prisms, 

 variously grouped. Molybdic acid is sometimes set free as liquid 

 globules, which coalesce, rise to the surface, and afterwards solidify 

 as small spheres. 



The Solar Heat. — M. Mouchat, who has been experimenting 

 on the utilization of the solar heat, has sent in a paper on this 

 subject to the Academy of Sciences. He states that, according to 

 his experiments, upwards of three-sixths of the solar heat might 

 be gathered at a small cost. At Paris, a surface of one square 

 metre normally exposed to the rays of the sun receives, on an 

 average, at any time of the year, on a fine day, ten units of caloric 

 per minute. Such a quantity of heat would make a litre of water 

 at freezing-point boil in ten minutes, and is equivalent to the 

 theoretical action of a one horse-power. He further states that 

 he had proved the possibily of keeping hot-air machines going by 

 means of solar rays, and had succeeded in making a few litres of 

 water boil by exposure to the same agent; and in June, 1866, 

 he had made a small steam-engine work by converting water into 

 vapour with the assistance of a reflector one metre square. 



The American Association for the Advancement of Science will 

 hold its eighteenth meeting at Salem, on Wednesday, August 

 18th. It is intended to give great prominence to microscopy, and 

 the committee have issued a special prospectus calling on micros- 

 copists to aid in sending instruments and specimens. Communi- 

 cations should be addressed to Mr. F. W. Putnam, the Local 

 Secretary, Salem, Massachusetts. The titles of papers should be 

 handed in as early as possible, in order to secure their presentation 

 to the Association. Each title should be written on a separate 

 slip of paper, with the author's name and address, and an esti- 

 mate of the number of minutes required to read the communica- 

 tion. As soon as practicable after entering the titles, the paper 

 itself, or an abstract, must be handed to the Secretary, and until 

 all these conditions are complied with, no title can appear in the 

 programmes. 



