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 jdividing 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 

 experimeijtal conclusions of the above-named philosopher. 



LXXXV. — On the Heat of Vapours and on Astronomical 

 Refractions. By John VV^illiam Lubbock, Esq., Treas. 

 R.S. F.R.A.S and F.L.S., Vice- Chancellor of the University 

 of London, Sfc. 



[Continued from p. 514.] 



ON THE STEAM-ENGINE. 



TpHE 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. 



— ^ — 1 



^ ~ q ~ n + qp^ 



in which g is the density of steam, p the pressure, and 7i and 

 q constants. According to my expression 



* Tfieorie de la Machine a Vapeur, p. 111. 



