42 Mr Buchanan, On a solar Calorimeter used in Egypt 



The main condenser is the tube KG, 12 inches long and 

 2 inches in diameter. Out of it at the top springs the boiler 

 tube G, B, A, E, of silver and J-inch in diameter. At E, and 

 from E to F its diameter is 1 inch, and this carries the steam 

 dome, which is a glass tube closed at one end and inserted into 

 the part EF, where it is fixed with a screw collar and washer. 

 The steam tube passes axially through the whole instrument, 

 terminating just inside of the glass dome. The steam condensed 

 in it runs out at the lower extremity L and is received in a 

 graduated tube in which it is measured or weighed. The glass 

 reservoir Z, which is shown hanging from the outside rim of 

 the reflector, is connected by an india-rubber tube with the 

 bottom of the condenser and the instrument becomes a U-tube, 

 of which the reservoir and india-rubber connection are one limb 

 and the condenser and boiler the other. The instrument is thus 

 easily filled with water and the height at which it stands in the 

 space EF is regulated by means of Z. 



When the instrument is going to be set in action it is pointed 

 axially to the sun. When in this position, the tube EF throws a 

 strong circular shadow on the top of the main condenser CB, and 

 concentric with it. With the rotation of the earth the axis 

 moves away from the direction of the sun and the shadow be- 

 comes eccentric. The appearance of eccentricity strikes the eye 

 at once, and it is rectified by a slight motion of the instrument 

 round its polar axis. The instrument requires adjustment every 

 two or three minutes. 



When pointing truly to the sun all the rays which strike the 

 reflector are reflected on the length AB of the axis. But the 

 boiler tube having a radius of ^-inch intervenes and receives 

 these rays on its blackened surface. The rays reflected from the 

 inner extremity of the inner mirror are reflected on a part of the 

 boiler tube a little below the line BB 2 , and those reflected from the 

 outer extremity of the outer mirror are reflected on a part of 

 the boiler a little above the line AB 3 . This is due in both cases to 

 parallax. 



When the sun's rays strike the surface of the boiler, those 

 that are not thrown back again are absorbed by its blackened 

 surface and passed by conduction through the metal to the water 

 which occupies the space round the steam tube. When every- 

 thing was at the temperature of the air, and the instrument 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 



