2 REPORT—1849. 
municated by the pressure of the steam, leaving 890° as the true heat of vaporization 
of water. In a perfect steam-engine, supplied with water at 212° and worked at 
atmospheric pressure without expansion, 965° will be the heat communicated from 
the fire to the boiler, 75° will be the heat utilized by conversion into force, and the 
remainder, 890°, will be the heat given out in the condenser. 
By working the steam expansively, so as to utilize its sensible heat, the ceconomi- 
cal duty may be at least doubled. In this case 150° out of 965° communicated to 
the boiler will be converted into force, leaving only 815° to be evolved in the con- 
denser. 4 
On De Vico’s Comet. By the Rev. Prof. Powe, F.R.S. &e. 
The author called the attention of the Section to the expected return of this comet, 
the first since its discovery. It will come to its perihelion on Feb. 6, 1850, but will 
be in such a position with respect to the earth as probably to render it quite invi- 
sible. The annexed diagram gives a rough idea of its positions. 

~ 
— ~ 
Se ——— 
PATON TP 


gust 
De Vi'co's Comet 

Prof. Chevallier has since printed an Ephemeris of the comet: the only period ; 
during which it could possibly be seen would be in October 1849. 
On a new Equatorial Mounting for Telescopes. 
By the Rev. Prof. PowE.r, F.R.S. &e. 
The object of the plan here proposed is mainly the personal convenience of the 
observer, and the ease and rapidity of changing to a new position, which is oftena 
matter of more importance than mere comfort, ; 
