[NTENSITT OF CORONAL LIGHT DURING THE SOLAR ECLIPSE OP 1886. 369 
the lamp illumination by the plan actually employed had been ascertained for varying 
resistances it became a matter of no moment. The galvanometer used in this case was 
one of Thomson’s ammeters, made more sensitive by fixing a permanent magnet along¬ 
side the usual magnet, so as partially to neutralise its magnetism. By this plan a 
very small change in current gave a large deflection, or at all events a deflection which 
was readable. By reproducing these deflections under exactly similar conditions the 
illuminating value of the lamp could be measured in the ordinary way. 
The second instrument, which we shall call the integrating box, for measuring the 
total coronal light with as little light from the sky as possible, was constructed on the 
same principles. It consisted merely of a long deal box coated internally with lamp¬ 
black, in which a screen with a large grease spot was inserted at S. There was a 
similar slot for the lamp as in the other instrument. The end A was, however, open, 
and during the eclipse it was placed at such an angle that the axis of the tube pointed 
to the centre of the Moon. The aperture, 0, for making the observations was in this case 
also covered with a black velvet cloth, under which the head of the observer was placed. 
The third piece of apparatus consisted of an ordinary Bunsen bar photometer, 
60 inches in length, with movable disc, made by Messrs. Alex. Wright and Co., of 
Westminster. As originally arranged, it was fitted for two standard candles; for 
the purpose of the eclipse observations, these w'ere replaced by a small glow lamp. 
As the plan of the photometric work contemplated by us depended for its execution 
upon such assistance as we were able to get out at Grenada, it was arranged that we 
should take advantage of the kind offer of service made by Captain Archer and the 
ofiicers of H.M.S. “ Fantome,” which had been told off to assist the expedition, and 
make the observations at some spot in convenient proximity to the anchorage of that 
vessel. As the latter end of August falls during the hurricane season in the West 
Indies, it was desirable to moor the “Fantome” in the most secure anchorage in the 
island, viz., in Clerk’s Court Bay, wFich is at the south end of Grenada. It appeared 
from the charts that a suitable station might be found on the southern end of Caliveny 
Island, distant about mile from the spot which would be made use of as the anchorage. 
Caliveny Island was accordingly included in the list of stations provisionally selected 
by the Eclipse Committee of the Eoyal Society, and submitted to the Governor of 
Grenada. Mr. Sendall and Captain Hughes were kind enough to visit the spot, 
and they reported thah a fairly good station might be obtained on the extreme end of 
the island, but that difficulties might be experienced in landing the apparatus. 
Captain Archer deemed it prudent, therefore, to make a preliminary survey of the 
MDCCCLXXXIX.-A. 3 B 
