THE SOLAR ECLIPSE OP 1898 . 
255 
bands. These are seen just at the moment of totality arid are some¬ 
thing like the reflection of a ray of light from a water surface disturbed 
by ripples. They appear to move over the ground, but are better seen 
on a white background such as a wall or side of a house. Attempts 
have been made to photograph them, but hitherto without success, and 
I would suggest them as a good subject for the amateur photographer. 
The lens must be one of large aperture, since the amount of light 
available is small and the exposure, owing to the rapid movement, must 
be almost instantaneous. A whitewashed wall, if in proper position 
opposite to the sun, would do well as a background, or if this be not 
available, a tightly stretched sheet would do as well or better. 
In hill stations, where a large extent of country can be seen, the 
amateur observer would do well to watch the most impressive pheno¬ 
menon connected with an eclipse, the approach of the moon’s shadow. 
To do this to advantage he should watch the sun till the eclipse is 
nearly total, and then, turning his back to the sun, look at the advancing 
shadow. If lie is in a position to get a very distant view, such as no 
doubt could be obtained at stations at the north end of the line, from 
which the slopes of the Himalayas can bs seen, it would be quite worth 
while to try to get a photograph of the landscape showing the moon’s 
shadow on the earth. This presents no difficulties, and any amateur 
photographer who is lucky enough to find himself at a suitable place 
could undertake it. Such a photograph would have no great scientific 
value, but would form an interesting record of the eclipse. 
Attempts to draw the corona are not of much value; anyhow, in 
the case of inexperienced observers. The same is true of observations 
made with an ordinary telescope which will not show much more than 
can be seen with the naked eye. Those who possess telescopes will, 
no doubt, set them up for use, and if the air be particularly clear it is 
possible that some fine coronal details may be seen. 
The observer may, of course, try to draw these, but such drawings, 
even if made by a skilful draughtsman, will have but little value as 
compared with photographs. 
We now come to the question of the amateur astronomer who wishes 
to photograph the eclipse. Let us consider what chance he has of 
success. The ordinary photographic camera and lens, on account of 
the short focal length and consequently small image of the sun, is not 
of much value. An approximate rule for calculating the size of the 
sun’s image on the plate is that 'it is -^inch diameter for 1 foot focal 
length of lens. A whole plate lens will therefore only give a sun about 
r 2 inch diameter on the plate, which is obviously too small to show 
much detail. We must therefore enlarge the image, which can be 
done either by increasing the focal length or by placing a negative 
lens behind the principal as is done in the case of the so-called 
telephoto combination. 
As a means of increasing the focal length we may remember that with 
the ordinary rectilinear doublet the focal length of each of the lenses in 
the combination used singly is twice that of the whole combination. The 
optical distortion introduced by using only a single lens would be of no im- 
