ofSnozv around Plants. 249 



of the air, will allow ; and upon reflecting that the influence of 

 solar heat, whether direct or diffuse, continues during the whole 

 day, we here discover the cause of the greater or less degrees of 

 melting which are produced around stakes, &c. of different sizes, 

 and which, far from being in proportion to the mass of matter, 

 as would occur if these substances were heated to the same tem- 

 perature previous to their being implanted in the snow, follow, 

 on the other hand, within certain limits, the inverse ratio of the 

 diameters. 



But here we enter upon the development of theories which have 

 long been known ; and the object of this communication was 

 to submit to the judgment of natural philosophers a particular 

 explanation of certain general principles which have only re- 

 cently been introduced into the science of heat. 



Notice of a Dioptric Light erected at Kirkcaldy Harbour, with 

 Description of the Apparatus for cutting the Annular Lens to 

 the true optical figtire* By Edwaud Sakg, Esq. F.R.S.E., 

 Civil Engineer, Edinburgh.-j- Communicated by the Society 

 of Arts. 



The harbour of Kirkcaldy, like the greater number of har- 

 bours on the coast of Scotland, is tidal, being left completely 

 dry even at the ebb of neap tides. The larger class of vessels 

 which frequent the port, can only enter the harboin* at or near 

 the stream; and thus the increased commerce of the place had 

 rendered it an object of some importance to have the entrance 

 thoroughly lighted. 



• Read before the Society for the Encouragement of the Useful Arts in 

 Scotland. 



t Report of the Committee to whom it was remitted to consider of Mr 

 Sang's paper, relative to a Dioptric Light erected at Kirkcaldy Har- 

 bour. Read 25th April 1«38. 

 Mr Sang's invention of grinding annular surfaces of any form by means of 

 cutters attached to a moveable arm, whose end is guided by a spring uncoil- 

 ing itself from the evolute of the curve surface which the lens requires, is 

 novel and ingenious ; and if equally applicable to the construction of instru- 

 ments requiring great accuracy of form, promises to be extensively useful. 

 The mode of giving any required direction to the scratches or small indenta- 



