562 Mr. Lubbock on the Heat of Vapours 
appears to open a field for discovery, which experimental 
industry cannot fail to cultivate with immediate success. 
Note . — On the evening of the meeting at which my investi- 
gations were presented to the Society, my friend. Dr. Bache 
of the Girard College, gave an account of the investigations 
of Professor Ettingshausen of Vienna, in reference to the im- 
provement of the magneto-electric machine, some of the re- 
sults of which he had witnessed at the University of Vienna 
about a year since. No published account of these experi- 
ments has yet reached this country, but it appears that Pro- 
fessor Ettingshausen had been led to suspect the develop- 
ment of a current in the metal of the keeper of the magneto- 
electric machine, which diminished the effect of the current 
in the coil about the keeper, and hence to separate the coil 
from the keeper by a ring of wood of some thickness, and 
afterwards, to prevent entirely the circulation of currents 
in the keeper, by [dividing it into segments, and separating 
them by a non-conducting material. I am not aware of the 
result of this last device, nor whether the mechanical diffi- 
culties in its execution were fully overcome. It gives me 
pleasure to learn that the improvements, which I have merely 
suggested as deductions from the principles of the interference 
of induced currents (76), should be in accordance with the 
experimental conclusions of the above-named philosopher. 
LXXXV . — On the Heat of Vapours and on Asti'onornical 
Refractions. By John William Lubbock, Esq.^ Treas. 
R.S. F.R.A.S and F.L.S., Vice-Chancellor of the University 
of London^ ^c. 
[Continued from p. 514.] 
ON THE STEAM-ENGINE. 
^1 "'HE law which connects the pressure and the temperature 
of steam having been unknown, various empirical rules 
have been given. As, however, the expressions which arise are 
not in a convenient form for the calculations which are re- 
quired in order to ascertain the duty which steam-engines are 
capable of performing, or to solve other problems of the same 
nature, M. de Pambour*, in his work on that subject, has 
employed another expression, viz. 
- J_ — 1 
^ “ T 
in which q is the density of steam, p the pressure, and n and 
q constants. According to my expression 
* Theorie de la Machine a Vapeur, p, 111. 
