372 CAPTAIN W. DE W. ABNEY AND DR. T. E. THORPE ON PHOTOMETRIC 
5. At 6.30 connect up all leads, see that your lamp works properly, and that the 
intensit}^ of the light responds to the screw of the resistance apparatus. 
G. The back edge of the wooden piece carrying the lamp may he conveniently 
placed at Division 50 of the graduated scale. This, with the resistance apparatus 
open, will probably give you more light than you require. If at the moment of 
totality, and with the lamp full on, the coronal light is greater than that of the glow 
lamp, push up the lamp to Division 30. If you have occasion to move the lamp 
from 50 (which is very improbable), be very careful to note the particular distance 
from the screen at which you place it. 
7. At 7'0 request Mr. Webb and the man who records his readings to take up 
their stations at the cement slab. Take up your owm position at the integratiug box. 
Mr. Webb’s position to be such that he readily hears your command to read. 
8. As the light decreases just before totality, that is between 7.0 and 7.10, turn 
the light up or down with the screw, so as to follow the decrease, so that after the 
moment that totality begins you may be aide to begin your comparisons -with the 
least possible delay. 
9. Intimation that totality has begun will be given to the party by Quartermaster 
Follett, who will call out 230. At intervals of 15 seconds he will call out the 
number of seconds still to elapse before totality ends. 
10. When you have made your adjustment by the screw as carefully as you can, 
call out “read” to Mr. Webb; do not turn the screw again until you hear him give 
his reading to the man who records. Again work the screw, make a second adjust¬ 
ment, and again call out “read,” and again wait until Mr. Webb has given his reading 
before you begin again. If this point is not attended to, the needle will be’ in such 
rapid oscillation that it will be impossible to get an accurate galvanometer reading. 
11. Experience shows that 12 readings may be taken in 100 seconds, but it is not 
advisable that you should attempt to make more than 12 comparisons during 
“ totality.” Recollect that a ferv readings carefully and deliberately done are worth 
far more than a large number made hurriedly. Do not touch the position of your 
lamp at the end of your observations.* 
12. Be careful not to fatigue your eye by looking too much at the Sun during the 
hrst stage of the eclipse. Insist that all talking ceases after 7. 
Instructions to Lieutenant Bairnsfather, [Bar Photometer.) 
1. The eclipse begins at 6hr. 12m. ; totality commences at about 7]n’. 10m., and 
lasts about 230 seconds. 
2. It is desirable that you should be ashore not later than 6 a.m. (It is assumed 
that your photometer bar. leads to galvanometer and to glow lamp, stand for galvo.no- 
* This instruction was given in order that iJre position of the lamp might be verified after the 
observation:; wmre concluded, 
