42 Mr Buchanan , Ow a solar Calorimeter used in Egypt 
The main condenser is the tube KC, 12 inches long and 
2 inches in diameter. Out of it at the top springs the boiler 
tube C, B, A, E , of silver and f-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 
