406 The solar Eclipse of April 17, 1912 



were not required. Very fortunately I 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 milli- 

 metres, and they consist of one green glass 3 millimetres 

 thick and two pink glasses, the external one being 2\ and 

 the internal or middle glass being \\ millimetres thick. 

 These seem to be pieces of the same glass, and differ from 

 each other only in thickness. 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 en- 

 croachment on the periphery of the sun became less and 

 less, though the augmentation of the area eclipsed proceeded 

 rapidly. 



At 1 1 h. 35 m. 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 1 1 h. 50 m., there was an impression of approaching 

 nightfall. 



At 1 1 h. 40 m. 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 1 1 h. 45 m. it became 

 somewhat ogival, and by 1 1 h. 50 m. 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 



