INTENSITY OF CORONAL LIGHT DURING THE SOLAR ECLIPSE OF 1893. 435 
expressed in terms of Siemen’s amyl-acetate lamp, in the case of the two lamps 
actually employed, is seen from the following tables. 
Lamp C 6. Used with the Equatorial Photometer. Mark 184 D. 
Amperes. 
Light units. 
Amperes. 
Light units. 
Amperes. 
Light units. 
0-8 
•004 
1-00 
•030 
115 
T02 
0'85 
•0065 
101 
■034 
1-20 
•140 
0-9 
•0100 
105 
•048 
F25 
•193 
0-95 
■017 
1-10 
■073 
1-30 
•262 
Lamp C 3. Used with the Integrating Photometer. Mark 185 D. 
Amperes. 
Light units. 
Amperes. 
Light units. 
Amperes. 
Light units. 
0'S 
•002 
1-00 
•026 
1-20 
•093 
0-85 
•005 
105 
•035 
1-25 
•125 
090 
•010 
1-10 
•048 
1-30 
•167 
095 
■017 
115 
•066 
The readings of current strength in the case of the equatorial photometer were 
made by means of a Weston ammeter, which is especially convenient for the purpose. 
In the case of the integrating instrument an Evershecl ammeter was used. These 
were procured for us by Professor Ayrton, and were carefully tested by him in order 
to ensure that their indications were strictly comparable. He was also good enough 
to select the glow-lamps for us and to have them standardised in his laboratory. On 
again standardising them after making use of them for the observations they were 
found to be practically unchanged. Our best thanks are due to Professor Ayrton 
for the interest he displayed in our work, and for the great amount of time and 
trouble he spent on our behalf. 
As regards the rest of the work, nature of battery, instructions to observers, &c., 
the details were identical with those already given in our previous paper. 
The Joint Committee representing the Poval Society, the Royal Astronomical 
Society, and the Solar Physics Committee of the Department of Science and Art, 
which was charged with the superintendence of the arrangements for observing the 
Eclipse of April 16, 1893, directed that the photometric measurements of the coronal 
light should be part of the work of the expedition to be despatched to Senegambia. 
Professor Thorpe (who was in charge of the expedition) was entrusted with the 
equatorial photometer measurements, and was assisted by Mr. P. L. Gray, B.Sc., 
who undertook the galvanometer readings, whilst the observations with the inte¬ 
grating photometer were to be made by Mr. James Forbes, jun., of the Royal 
College of Science. 
3 k 2 
