The Total Solar Eclipse of 1900. ae 
displacement of the plunger p in the opposite direction to that in which the lever 
is working. 
The actual result is, that during the upward motion of the lever the right- 
hand drum is stationary, and the full beam of light forming the spectral image 
is concentrated on one of the six plates mounted on it; at the same time the left 
drum, on which no light is falling, is being turned into a new position, to be 
ready for the next exposure. Just before the end of the upward stroke the 
plunger p is forced quickly down, and the beam of light is transferred to the 
left drum, which has just been brought into position ; but for a small fraction of 
time the spectrum is actually exposed on both plates, 7.e. the lower plate on one 
and the upper on the other. As the motion of the mirrors is strictly in their 
own planes, this motion has no effect on the position of the images on the plate, 
and consequently does not, if properly adjusted, impair the definition. 
IV. 
Dr. A. A. Rampautr’s REporRT. 
The object of the spectroscopic observations undertaken by us was to obtain 
two series of spectra, at second and third contacts, with the idea of determining 
the order in which various lines appeared in, and faded out of, the flash and 
chromospheric spectra. 
It was at first proposed to use a slit spectroscope, on an equatorial mounting, 
and to project a very narrow spectrum upon a uniformly-moying plate. With 
such an instrument, if the slt were kept continually tangent to the advancing 
limb of the Moon, a continuous record would be obtained, beginning at one end 
with the ordinary solar spectrum merging into the flash, and from that into the 
spectrum of the corona. 
What we chiefly desired to test was, whether the change from the absorption 
spectrum to the ‘flash’ spectrum took place simultaneously for all the lines, or 
whether some became reversed earlier than others, as might be expected to occur 
if the absorption of different lines took place at different depths in a reversing layer. 
This method would, however, have required a good equatorial mounting, 
and very accurate clockwork, to enable the observer te keep the slit tangential 
to the Moon’s limb during the whole period. 
For a long time it was very uncertain whether I could join the expedition, 
and it was not till the middle of April that I definitely decided to go. It was 
then too late to procure the necessary telescope, equatorially mounted; and 
accordingly a less complicated instrument, which could be more rapidly con- 
structed, was substituted for it. 
This instrument, designed and constructed by Sir Howard Grubb, consisted 
