at the total solar Eclipse in 1882 363 



a pair of spectacles is too insignificant to cause any incon- 

 venience. 



Discussion of Observations. 



The observations made with the calorimeter on the i6th, 

 1 7th and i8th May are given in detail in Table III and they 

 are represented graphically in Fig. 8. On the i6th the 

 distillate was received in a cylinder capable of holding over 

 100 c.c. and graduated into single cubic centimetres. In the 

 two columns for rates on this day, the one is the rate per 

 minute while 10 c.c. were collected, and the other the rate 

 per minute while 20 c.c. were collected. On the i/th and 

 1 8th a tube graduated into half cubic centimetres and holding 

 20 c.c. was used. Time was taken as every 5 c.c. were collected, 

 and the tube was emptied when 20 c.c. had been collected. 

 The readings for every 5 c.c. were made without removing the 

 receiver from the distilling tube. The portion of 20 c.c. was 

 measured in a truly vertical position and is more exact than 

 the measurement of its constituent portions of 5 c.c., although 

 every care was taken to note the time when exactly 5 c.c. had 

 run without running the risk of losing any of the distillate. 



The most important manipulation is attending to the 

 equatorial motion of the instrument. The observed rate of 

 distillation agrees the more closely with the true rate the 

 more carefully the axis of the instrument is kept pointed 

 towards the sun. This was controlled by observing the 

 shadow of the steam space on the top of the condenser with 

 which it is concentric. 



The position was adjusted every two or three minutes 

 when it was usually put a shade in advance of the true 

 position so as to give it a position correct for the middle 

 of the interval. 



The calorimeter ought always to be fed with pure distilled 

 water. Unfortunately this was not available, and Nile water 

 had to be used. It contains a considerable amount of earthy 

 carbonates and is apt, after prolonged use, to froth. With 

 the glass dome, however, this was at once detected, and if it 

 was serious the water was changed. 



