14 



THE NATURE BOOK 



the filaments twisted and twirled about 

 as if the sky had been smeared here and 

 there. 



It was evidently such a scene as this 

 that is referred to in the old weather-lore 

 saying : 



" Trace in the sky the painter's brush. 

 The winds around vou soon will rnsli." 



and in order to screen the lens from the 

 sun, which was right in front of the 

 camera, a shade was held over the ob- 

 jective. Although the greater and more 

 distinct portion of the cloud in the pic- 

 ture is alto-cumulus, the cirro-stratus will 

 be observed in streaks radiating from 

 the horizon-like spokes from the hub of 



CIRRO-STRATUS CLOUD FORMING A SOLAR HALO. 

 This photograph was taken in the same direction but a few minutes after that reproduced at the top of p. 13. 



At these altitudes we find also the 

 cirro-stratus clouds. This consists, as a 

 rule, of a thin, whitish layer, which at 

 times covers the whole sky and makes 

 the sky appear whitish instead of blue. 

 Such a cloud is responsible for the beau- 

 tiful halos — sometimes single, sometimes 

 double — which are seen at times encircling 

 the sun with radii of different lengths. 



Such a cloud does not lend itself at 

 all to photography. At times, however, 

 it is not homogeneous, but presents the 

 appearance of straight streaks, which 

 converge towards the horizon or a tangled 

 web. It is then that the camera can be 

 used with effect, as the photograph 

 at the top of p. 13 will show. This was 

 secured on June 23rd, 1907, at 1.23 p.m., 

 at South Kensington. The camera was 

 pointed in the direction of south-west, 



a wheel. As the wind, which was strong 

 at the time, was south-west, both types 

 of cloud gradually passed overhead. 

 Eventually the alto-cumulus passed nearly 

 out of the field of the camera, as can be 

 seen from the illustration on this page, 

 while the cirro-stratus was still blowing 

 up. The latter was the cause of a most 

 brilliant halo, which is depicted in this 

 illustration, the camera not having been 

 moved between the two exposures. The 

 streaky appearance of this halo is due 

 to the strii)y nature of the cirro-stratus. 

 The position of the sun can easily be 

 determined by finding the centre of the 

 circle which forms the halo. 



It seems to have been generally con- 

 ceded that solar halos indicated the advent 

 of wet weather, for one old saying runs 

 as follows : 



