434 CAPTAIN W. DE W. ABNEY AND DR. T. E. THORPE ON PHOTOMETRIC 
moon’s disc was made to fall exactly within the circle. As the telescope was equa- 
torially mounted with clockwork, the image could be kept stationary within the 
circle. The screen was of Rives’ paper of medium thickness, and round the pencilled 
circle a series of small grease-spots about of an inch in diameter were made. For 
the mode of making the grease-spots and testing the screens we may refer to our 
original paper. Fig. 1, reproduced from this paper, shows the screen mounted in its 
circular frame. The screen could be rotated so as to bring the spots into any desired 
angular position, and it could be removed at pleasure by releasing it from the 
buttons which held it within the frame. The box to hold the screen in the focus 
of the telescope and the Varley carbon resistance-apparatus used to increase or 
diminish the light of the standard glow-lamp were identical with those employed 
during the 1886 eclipse, and are described in our previous paper (loc. cit., pp. 367, 
et seq.). 
Fig. 1. 
The most important variations in the mode of making the observations, as compared 
with the previous measurements, consisted in the manner of connecting up the lamp, 
resistance-apparatus, and galvanometer, and in the method of reading the current- 
strength. On the former occasion the brightness of the lamp was increased by adding 
resistance to the shunt; consequently in the measures made the highest readings ot 
the galvanometer corresponded with the lowest intensity of light. On the present 
occasion the better plan of putting the galvanometer and resistance in the main 
circuit was employed ; hence high readings of the galvanometer mean high intensities 
of light. The lamps used during the present eclipse were Edison-Swan’s 8 volts, 
5-candle power. The relation between the current-strength and light intensity 
