38 Mr Buchanan , On a solar Calorimeter used in Egypt 
very well chosen. The eclipse was total at 8.34 a.m. on the 17th May, 
1882, civil reckoning. The maximum duration of totality that 
was expected was 70 seconds, and in fact it lasted longer than 
65 seconds. 
The expedition arrived on the 8th May, and I was able to 
begin work with the calorimeter on the 11th. As the instrument 
was new in every way the work of the first few days was mainly 
directed towards learning the manipulations and finding out and 
rectifying defects. The instrument worked at once much more 
satisfactorily than I could have expected, and the only important 
alteration which had to be made was to replace the original metal 
dome as steam space by a glass tube. This performed the functions 
of a gauge-glass, a steam space and a guarantee against priming. 
It is of course essential that nothing but condensed steam should 
arrive in the receiver, and with the glass steam dome this can be 
assured. Improvements of one kind or another were made every 
day up to the loth. On the 16th, 1 7 th and 18th experiments 
were carried out with the apparatus in best working order and 
under very favourable circumstances. They are collected in 
Table III. The observations made on the morning of the 17th im- 
mediately after the total phase of the eclipse are given separately in 
Table IY. The instrument was constructed and was taken out to 
Egypt for use under ordinary conditions. Its exposure during the 
later phases of the eclipse was not originally contemplated, yet 
the results are full of interest. 
The observations were made on the 16th, 17 th and 18th May. 
The sun’s declination at apparent noon was 19° 8', 19° 22' and 
19° 35' on these days respectively. We take the mean declination 
for the period as 19° 22' N. 
The latitude of the station being 26° 37' N. the mean meridian 
altitude of the sun was 82° 45' = 82*75°. Table I. gives the sun’s 
altitude and azimuth at noon and at every half-hour on each side 
of noon until sunset. These data were obtained graphically by 
measurements on the globe. It will be seen that when the sun is 
more than one hour from the meridian its altitude changes at the 
rate of about 6*5° in half an hour. When the altitude has fallen 
to 45° about 3£ hours from noon, the water of the boiler has begun 
to invade the glass steam dome owing to the inclination which it 
is necessary to give the instrument in order to keep it pointed 
towards the sun. This does not prevent the instrument acting 
perfectly well, as will be seen, in Table III., from the observations 
made on the afternoons of the 17th and 18th, but it is necessary 
to watch the operation very closely. Moreover, the principal object 
of the observations is to find the maximum distilling effect of the 
sun, and this is not likely to occur when it is more than three 
hours either before or after noon. The period during which, if 
