356 
REV. S. J. PERRY OX THE TOTAL 
great importance to test thoronglily so interesting a fact, and Professor Tacchtxi 
joined the British Expedition at Southampton with the mtention of placing, if 
possible, this question beyond the region of doubt. The instructions to Lieutenant 
ITelby were to place the slit of the spectroscope exactly on the inner edge of the 
corona at the commencement of totality, and then to move it successively to distance 
OT, 0*2, 0’3, 0’4, and 0‘5 of a diameter from the dark surface of the Moon, repeating 
afterwards at the Sun’s pole what first was done near his equator. To avoid rotating 
the spectroscope, the slit w^as placed radial at the solar equator, and tangential at the 
poles. The same portion of the spectrum remained always in the field of view during 
the whole of the observations, and embraced rather more than the distance from 
W.L. 5600 to h, comprising, therefore, the positions of the two principal bands of the 
carbon. To fix accurately the place of any lines visible, photographs of the solar 
lines in the portion of the spectrum required had been taken at Stonyhurst on plates 
stained with eocine, and on others kindly sent by Captain Abnev^, Pt.E. As these did 
not come out distinct enough to use safely with a feeble illumination, a number of the 
jDrincipal lines in the field of view were measured with a micrometer, and then 
mapped on a large scale and reduced photographically to the scale required. Trans¬ 
parent scales graduated to tenths of millimetres were also prepared, so as to be ready 
for any change that might be recpiired. 
On August the 26th, between 6 and 7.15 A.M.. we had the first all-round practice 
with every instrument in position, with all hands on shore who were to take part in the 
observations on the 29th, and each thing done just as if the eclipse had been taking 
place. The time was called every ten seconds by Bobert Smith, A.B., coxswain of 
tlie captain’s cutter, in a loud and distinct tone, that could be heard easily by all present. 
John Collum, signalman of H.M.S. “ Bullfrog,” and other reliable seamen, noted 
down the observations as these were called out, and afiixed the corresponding times. 
All was found to work wmll, and not a few useful lessons were learnt for the mornino- 
of the 29th. Later on in the day, whilst observing with the grating, I found the. 
heat so intense that I was forced to leave the instrument for a time and retire to the 
house. On my return I perceived at once that some inquisitive looker-on had been 
gently feeling the grating with his greasy finger, probably to ascertain its degree of 
smoothness. My dismay at first was great, as I was afraid I might have been obliged 
to abandon the grating in favour of the Hilger direct-vision prisms, with which I had 
supplied myself in case of accident. I removed part of the roof of my observing hut, 
in order to test the grating thoi’oughly, and I was satisfied at last that the spectrum 
showed no signs of being in the least affected by the stain left by the finger on 
the surface of the ruled metallic plate. I resolved, therefore, to retain the grating ; 
but, finding that the second order of spectrum with a power of 4 gave a more brilliant 
picture than the first order with the power of 6^, I made up my mind to adopt the 
second order for the clay of the eclijjse, although this necessitated the sacrifice of the 
