in diameter and four inches long—by eee! 
to the open ends and drilling a hole throu 
which a glass stopper may be fitted. 
Finally the apparatus may be with a little additional expense 
so coustructed that it can also be used for projecting photographic 
transparencies after the principle of the magic lantern. Small 
photographs on glass may thus be used in place of diagrams and 
the great geological features of our globe, the glaciers for exam- 
ple, may in this way be brought before the eyes of an audience 
with almost all the vividness of the reality. The same meth 
og 
3 
cie 
dark lines of the solar spectrum is to take a photograph of the 
i ge on the wall. 
Such photographic transparencies are easily made; but as few 
? 
teachers have the means or time for such work, it would be well 
ig 
J. Duboseq of Paris, after the plan of Foucault, and we find that 
it works very well. : 
Most of the apparatus here described is so simple that it cau 
be made by any good mechanic and for this reason we have en- 
tered into more detail than would otherwise be necessary. The 
lenses and other accessories must of course be purchased. The 
apparatus can also be ordered from E. S. Ritchie & Co. of Boston. 
Cambridge, August 8th, 1865. 
Ant. XXVII—On the use of the Bisulphate of Soda as a substilule 
jor the Bisulphate of Potash in the decomposition of minera’s, 
ily the Aluminous minerals ; J. LAWRENCE SMITH, 
pi Site sas by 
Professor of Chem., University of Louisville. 
