348 On a solar Calorimeter used in Egypt 



endless and it is probable that amongst the number of them 

 a combination will be found which is more efficient than the 

 first one that was tried. 



The Equatorial Mounting is shown in Fig. 4. The main 

 or central part is a piece of stout brass tube M, 4 inches in 

 diameter and 18 inches long. It is supported on an iron 

 tripod NN by an iron ring R in three segments which are 

 pinched together by screws 55. From the top edge of the 

 tube for 6 inches downwards a slot T is cut of rather over 

 an inch clearance, and a collar V, consisting of a length of 

 2 inches of tube that telescopes over the central tube, slips 

 up and down it and can be clamped in any position. The 

 slot is intended to receive the polar axis JS when adjusted 

 for latitude, the collar being clamped in the right place and 

 the weight X, which is much heavier than the calorimeter, 

 keeps the polar axis resting firmly on the collar. The polar 

 axis which is a tube of I inch diameter is pivoted round a 

 horizontal axis Y, which is also a piece of brass tube working 

 in bearings on the top of the central tube. When the tripod 

 has been set up so that the central tube is vertical the polar 

 axis is adjusted for latitude by a quadrant or protractor, or if 

 the pole-star is available, it is brought to be visible through 

 the tube which forms the polar axis. The calorimeter is held 

 by a collar W which surrounds it and is clamped on the 

 condenser tube. This collar is attached to a ball and socket 

 joint J which is carried by a piece of tube which fits tele- 

 scopically into the polar axis. The ball and socket joint was 

 found to be the simplest means of giving a motion for adjust- 

 ing the calorimeter for declination. We have thus a form of 

 equatorial mounting which is simple, effective, and cheap, as 

 it is almost entirely made out of brass tubes. 



Construction of the Reflector. In designing the reflector 

 actually used, the following determining conditions were 

 adopted. Length of focal line to be 2 inches ; angle of the 

 middle mirror to be 45 and its upper rim to have a radius 

 of 5 inches. With these data the 45 mirror can be completed 

 at once and the specifications of the outer and inner mirrors 

 follow by a simple graphical construction. The physical 



