Mr Kamtz's Meteorological Observations. 3S7 



fully in his Treatise on Optics. I have made several measure- 

 ments, and, when I divide into two parts the arc of the heaven 

 from the zenith to the horizon, the angk which that central 

 point of the heaven makes with the horizon was not 46° ; but it 

 varied a little according to circumstances, having an elevation 

 of about 20^ 



I made observations during fogs on the diameter of the vesi- 

 cular vapour, and convinced myself, by a comparison of one 

 hundred measurements of this kind, that the diameter depends 

 on the seasons being nearly double in winter to what it is in 

 summer. 



The phenomenon of a coloured ring around the shadow of the 

 head, when that shadow falls upon a cloud, as observed by 

 Bouguer, occurred to me several times. I made several measure- 

 ments of it, and the following is the most complete : On the 4th 

 of October a fog appeared in the south of the Valley of Grindel- 

 wald, and, having passed before the sun, I could observe a halo 

 by means of a blackened mirror ; the first circle red, had a radius 

 of 1"* 55'. Some minutes after, the fog being to the north of me, 

 and the sun shining brilliantly, I saw my shadow surrounded 

 by many coloured rings ; the radius of the first red circle was 

 about 1° 54'. These two measures give for the diameter of the 

 vesicular vapour about 0.00095 Fr. inch. Mr Kamtz also 

 made on a fine day, during each hour of the day, observations 

 with an instrument invented by Sir J. Herschell, named Actino- 

 meter, intended to measure the calorific power of the direct rays 

 of the sun. Mr Forbes of Edinburgh, who had entrusted him 

 with one of these instruments, made at the same time corres- 

 ponding observations with a second actinometer, at Brientz. 



Remarks on Boi'dcCs Geometrical Measurement of the Height 

 of' the Peak of Teneriffe. By Mr William Galbraith, 

 A. M. Communicated by the Author. 



A HE disagreement of the various late barometric measurements 

 of the height of the Peak of Teneriffe, made by careful ob- 

 servers, with good instruments, from the height deduced trigo- 

 nometrically by M. Borda, in 1776, induced me to examine 



VOL. XIV. NO. XXVIII. APRIL 1833. Y 



