NOTE ON SOME METEOROLOGICAL USES OF THE 



POLARISCOPE. 



By Louis Bell. 



Presented January 8, 1908. Received January 27, 1908. 



This is merely a preliminary notice of certain facts regarding atmos- 

 pheric polarization which may prove to have some prognostic value. 

 They were incidental to a proposed study of the character of autumnal 

 haze which the writer undertook last year at Mount Moosilauke, N. H. 

 This peak, 4811 feet high, has an almost uninterrupted sweep of horizon 

 over a radius of one hundred miles or so and offers an excellent chance 

 for investigating the distribution and nature of the haze that veils the 

 landscape in early autumn. For instruments I took along a Savart 

 polariscope, merely a Savart plate with a bit of tourmaline as analyzer, 

 an extemporized double-image polarimeter of the type outlined in the 

 early and valuable paper of Professor E. C. Pickering,^ a couple of 

 carefully calibrated photographic wedges for determining opacities, 

 and a direct vision spectroscope. 



A prolonged easterly storm, about the only thing which could have 

 defeated the program, cut short observations upon the summit, but a 

 week of preliminary observations at Breezy Point (elevation 1650 feet) 

 at the base of the mountain yielded results which seem to be of suffi- 

 cient interest to put upon record. 



These were made mostly with the Savart polariscope, an instrument 

 which, from its very wide field of view and great sensitiveness, showing 

 even one or two per cent of polarization, enables sky conditions to be 

 very readily investigated. The character of the sky polarization, with 

 its general symmetry and maximum in a plane at 90° solar distance, is 

 well known, but the nature and causes of its casual variations have not, 

 perhaps, received the attention that is their due. Nearly everything in 

 the landscape polarizes by reflection to a greater or less extent, the 

 more as the specular component of reflection is the greater. For 

 example, the glossy upper surface of a maple leaf polarizes strongly at 

 fairly large angles of incidence, while the mat lower surface has only 



* These Proceedings, 9, 1 et seq. 



