374 Trowbridge and Hayes—Application of 
made a mistake in writing down his figures—that he con- 
founded the cobalt with the iron percentage and vice versa. 
The sum 100 indicates that the analysis was done by difference. 
Had it been made directly and had the sulphur and copper 
been carefully determined the chances are the agreement with 
diately recognized as Breithaupt’s safflorite. It is exceedingly 
gratifying to find an analysis of a crystalline safflorite whic 
agrees so well (although, I must confess, in a peculiar way) with 
one of the massive variety and the meaning is at once evident. 
The specific gravity 7-167, together with the results of the 
chemical analysis, prove without a doubt that the heavy, gray 
and massive mineral sent me by Professor Weisbach and 
labeled schlackenkobalt is, indeed, safflorite, and the accom- 
panying tin-white smaltine d trates conclusively that smal- 
tine and safflorite do appear together and that too in precisely 
the manner indicated by Breithaupt in his Paragenesis. 
trust, then, that this article will serve to overthrow any doubt 
which may exist in the minds of mineralogists concerning the 
certainty of the existence of a massive variety of safflorite and 
that my views as here set forth may atone for any equiv’ 
statement or statements which may have inadvertently erept 
into my pamphlet. 
_ John C. Green School of Science, Princeton, N. J., Jan. 20th, 1885. 
Eo 
Art. XLVIIl.—Application of Photography to Electrical Meas 
by JoHn T 
urements ; ROWBRIDGE and HAMMOND VinToN 
HAYES. 
In the study of electromotive force and of voltaic cells it is 
often desirable to have long continued observations. The pes 
plete history of the action, for instance, of the Daniell cell w'¥’ 
