British Association for the Advancement of Science, 295 



tain, making certain simple allowances for temperature, the height 

 at which the barometer would have stood at the station on the 

 hill can be deduced ; and thence, by the usual calculation, the 

 height of the station. The stem of the instrument is previously 

 graduated, so that bare inspection shows the density of the air at 

 the elevated station. 



Sir D. Brewster communicated the following papers : " On a 

 new phenomenon of Color in certain specimens of Fluor-Spar." — 

 " On an Ocular Parallax in Vision, and on the law of visible di- 

 rection." — "An account of certain new phenomena of Diffrac- 

 tion." — "An account of an analogous series of new phenomena 

 of Diffraction when produced by a transparent diffracting body." 

 — ^^" On the combined action of grooved metallic and transparent 

 surfaces upon Light." These valuable papers called forth from 

 Sir J. Herschel the highest praise. " There is extreme difficulty," 

 said he, " in following with sufficient rapidity for discussion, such 

 an absolute torrent of new matter. Indeed, the discoveries of 

 Sir D. Brewster, whether viewed in relation to the intervals at 

 which they succeed each other, or the instruction they convey, 

 equally fill us with delight and astonishment." 



A paper on the Helm Wind of Crossfcll, was read by Rev. J. 

 Watson. 



Dr. Smith read a paper 07i the Variations in the quantity of 

 Rain which falls in different parts of the Earth. The causes 

 of these variations are, the' author imagines, to be ascribed to the 

 physical differences of the vicinity of each place, and in the track 

 of the most rainy winds ; and he found this opinion confirmed by 

 a long average of Westerly and Easterly winds at London, com- 

 pared with six other places. 



Prof Wheatstone read a paper on Binocular Vision, and on the 

 Stereoscope, an instrument for illustrating its phenoTnena. The 

 instrument is so named, from its property of presenting to the 

 mind the perfect resemblances of solid objects. A short explan- 

 ation of the principles of the instrument was offered by Prof. 

 W. Sir D. Brewster feared that the members could scarcely 

 judge from the very brief and modest account given by Prof W. 

 of the principle and of the instrument devised for illustrating it, 

 of its extreme beauty and generality. He considered it one of 

 the most valuable optical papers which had been presented to the 

 Section. He observed, that when taken in conjunction with the 



