46 Mr Buchanan, On a solar Calorimeter used in Egypt 



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

 central part is a piece of stout brass tube JI. 4 inches in diameter 

 and IS inches long. It is supported on an iron tripod JVJV by 

 an iron ring R in three segments which are pinched together by 

 screws .?;>'. From the top edge of the tube for six inches downwards, 

 a slot T is cut of rather over an inch clearance, and a collar Y con- 

 sisting 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 posi- 

 tion. 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 1 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 calori- 

 meter 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 telescopically 

 into the polar axis. The ball and socket joint was found to be 

 the simplest means of giving a motion for adjusting 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 Rejector. In desisting: the reflector actuallv 

 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 construc- 

 tion. The physical principle involved is that the angles at which 

 rays strike and are reflected from a mirror surface are equal. 

 The construction is shown in the diagram Fig. 5. On the straight 

 line OP which represents the axis of the instrument, lay off the 

 length AB = 2 inches ; this is the focal line. Through J. and at 

 right angles to AB draw Ax. and on it make AB S = 5 inches. 

 Through B draw BB 2 parallel to AB S and make BB 2 = 3 inches. 

 Join B*M 3 . BJB S is obviously the line representing the principal 

 section of the mirror inclined at 45 : to the axis. Its length 

 B 2 B i = \ 8 = 2 83 inches. If the line B 2 B 3 be continued until it 

 cuts AB produced in B 2 , then B Z B 2 is the generating line of the 

 complete cone of which the 45" mirror is a portion. Its length is 

 obviouslv \ 50 = 707 inches. The flat band which, when bent 



