344 ^ n a solar Calorimeter used in Ji^vpt 



everything was at the temperature of the air, and the instru- 

 ment was pointed to the sun at 2 p.m., the water boiled in 

 40 seconds, and it continued to boil so long as the instrument 

 truly followed the sun and as the sun was not obscured. This 

 operation had to be stopped when, in order to follow the sun, 

 the instrument had to be inclined at such an angle that the 

 water of the boiler began to trespass too far into the glass 

 dome. The greatest meridian altitude of the sun was 83, 

 and it was found inconvenient to follow the sun to altitudes 

 less than 45, so that the instrument was never used in a truly 

 vertical position. This has an advantage which will be 

 appreciated by the chemist, who always inclines a test-tube 

 when he is going to boil a liquid in it. The boiling proceeded 

 with perfect regularity even when the sun was at its hottest, 

 as on the forenoon of the 1 8th May ; and with the glass dome 

 as steam space everything could be followed minutely. The 

 steam developed in the boiler rises into the dome, from which 

 it finds exit through the inside steam tube GL. In it the 

 steam passes at least as far as B uncondensed, because the 

 temperature of the water boiling outside is slightly higher 

 than its own. But immediately it passes B it is surrounded 

 by water which at first is colder than itself and it is condensed. 

 In this process the steam gives out its latent heat and raises 

 the temperature of the water outside in the condenser corre- 

 spondingly, and the water produced from the steam runs 

 down the tube and is caught in the receiver. When steam 

 is in presence of water there is no delay in condensation so 

 soon as the temperature of the water is the smallest fraction 

 of a degree below the temperature of saturation. Therefore 

 so soon as the water which moistens the inside of the steam 

 tube has been cooled at all, it instantly condenses steam 

 sufficient in amount to raise its temperature to that of satura- 

 tion. The result is that the actual condensation of the steam 

 takes place at the upper part of the condenser and immediately 

 below the boiling space. As the instrument is to all intents 

 and purposes motionless and no circulation of water is main- 

 tained in it, the hot water remains at the top of the condenser 

 and from it hot feed is supplied to the boiler. While there 



