May 9g, 1912] 
NATURE 241 
LETTERS TO THE -EDITOR. 
(The Editor does not hold himself responsible for 
opinions expressed by his correspondents. Neither 
can he undertake to return, or to correspond with 
the writers of, rejected manuscripts intended for 
this or any other part of Nature. No notice is 
taken of anonymous communications.] 
The Solar Eclipse of April 17. 
Tue study of the article by G. Fayet in the Revue 
Scientifique of March 30, an account of which was 
given in Nature, convinced me that, with favourable 
weather, the solar eclipse of April 17 would prove to 
be interesting, although its totality was extremely | 
doubtful. a 
I went to Paris on Aprif16 and put up at the Gare 
du Nord. At to a.m. on April 17 I took a suburban 
train from that station to Eaubonne, which was on 
the central line, as shown in the map given in Fayet’s 
article. I arrived there about 10.35, and after look- 
ing round I took up a station at a seat by the road- 
side in front of the school. When I arrived the boys 
and girls were being dismissed, by order of the | 
Minister of Education, so that they might see the | 
eclipse. Some of them came round me while I was 
looking out for the first contact. They were much 
interested, and were very well behaved. They all had 
the red glasses supplied by an advertising firm, but 
they had a curiosity to see the sun through my glass, 
which showed it in its natural colour, and they were 
delighted with the effect. 
During the first hour they played about, because 
watching the gradual encroachment of the moon on 
the sun was tedious. When the diminution of day- 
light made itself felt they began to gather round me; 
so I told them they must not look at me but look at 
the sun and moon, and notice all that they saw, and 
that, while the eclipse was going on, they must not 
speak to me or to each other. ‘‘Ne pas parler?” 
“Yes,”’ I said, *‘ne pas parler—you must look and do 
nothing else.” They retired into the back part of the 
playground and stood in a group, and they no doubt 
looked, for they were quite silent. 
When the central phase was over and I had taken 
my glass away from my eyes, they rushed up in a 
body and surrounded me, and I asked them if the 
sun had become quite dark or if there had been some 
light all the time. Their opinion was divided. From 
this I concluded that the sun had been at no time 
completely obscured, for this would certainly have 
impressed them. 
As I was working alone it was useless to try to 
take the times of contact. Moreover, the second and 
third contacts, which are the most important, would 
happen so close to each other that, if I attempted to 
time them, it would interfere with my seeing what 
happened. I therefore devoted myself entirely to fol- 
lowing the eclipse and observing as well as I could 
everything that took place. It was certain that 
“Baily’s beads’’ would be a feature of the eclipse, 
and I had great curiosity to study them. 
The sky was cloudless and the sun very powerful. 
I had with me an ordinary binocular of low power, 
which I hoped: to find useful when the short-lived 
central phase, whether total or annular, arrived. In 
order to be able comfortably to follow the eclipse 
from the beginning to the end, I had the hand glass 
which pleased the school children. It was a com- 
bination of three coloured glasses measuring 110 x 35 
millimetres, so that the sun could be observed through 
it, using both eyes, whether it was used-alone or in 
conjunction with the binocular. 
NO. 2219, VOL. 89] 
The effect produced | 
by this combination of colours was that the sun, 
viewed through it, appeared of its natural hue. The 
density of the coloured medium was such that nothing 
but the sun’s direct rays penetrated it, and the sky, 
in which the sun appeared to be set, was quite black. 
I bought this glass of a hawker in the-streets of 
Barcelona on the eve of the total eclipse of August 30, 
1g05, and I found it very useful, although the interest 
of that eclipse centred almost entirely in the total 
phase, which lasted nearly four minutes, and during 
it reducing glasses were not required. Very for- 
tunately 1 was able to lay my hands on it before 
starting for Paris, and it was indispensable during 
the eclipse. 
The three glasses have an aggregate thickness of 
7 millimetres, and they consist of one green glass 
3 millimetres thick and two pink glasses, the external 
one being 23 and the internal or middle glass being 
14 millimetres thick. These seem to be pieces of the 
same glass, and differ from each other only in thick- 
ness. They have the same colour, which is very 
nearly that of a dilute solution of permanganate of 
potash. The colour of the green glass is a chromium- 
green, and the colour-intensity of its thickness of 
3 millimetres has been successfully compensated by a 
4-millimetre thickness of the pink glass. The result 
of the combination was most satisfactory. 
Having noticed that first contact had taken place, I 
settled down to follow the progress of the eclipse, and 
I continued making observations every five minutes. 
The rate of encroachment on the periphery of the 
sun became less and less, though the augmentation 
of the area eclipsed proceeded rapidly. 
At 11th. 35m. the eclipse appeared to be affecting 
the general illumination, and I looked round at. the 
school-house to the north of me. The ultramarine 
blue of the sky was getting darker and more of an 
indigo. Looking towards the horizon, which was 
masked by trees, the illumination was becoming 
decidedly fainter. The indigo colour of the sky spread 
round and became deeper as the eclipse went on, 
and, by 11h. 5om., there was an impression of ap- 
proaching nightfall. 
At 1th. 40m. the invasion of the sun’s disc had 
reduced it to a crescent with very sharp cusps. The 
limb of the moon still looked quite circular, but at 
1th. 45m. it became somewhat ogival, and by rrh. 
50m. this effect was very marked. By this time the 
schoolboys were observing the sun without coloured 
glasses. 
I now noticed the peculiar appearance of the 
shadows of the foliage of a tree cast on the ground 
close to my station. I also noticed that the illuminated 
surface of the dusty playground became more and 
more sombre, while the shadows under the — trees 
preserved the same tone, so that, while the illumina- 
tion of the exposed ground diminished rapidly, that of 
the ground in the shade of the trees had- already 
nearly reached its minimum of illumination before 
the eclipse was complete. 
After this my attention was confined entirely to 
what was taking place in the sky. I was now using 
the binocular with the reducing glass in front of the 
eyepieces. With it the rapid diminution of the 
luminous crescent could be easily followed and the 
view furnished was very sharp. 
As the area of the luminous crescent diminished 
rapidly before the advance of the dark lunar disc the 
colour of its light suddenly changed to red. This 
suggested to me that a brilliant display of protuber- 
ances might be expected. The tone of the 
red reminded me, at the moment, of that of 
nitrous fumes escaping into the air; it was 
therefore a very pure red. It became visible only after 
