( 53 ) 



Postscript to Description of Mr T All's Portable Diorania^ which 

 may be viewed by a number of persons at a time ; on pa^e 

 275 of the preceding volume. Communicated by the Royal 

 Scottish Society of Arts.* 



The quantity of extraneous light seen by the spectators, 

 under the arrangement described in that article, is much 

 diminished, and the effect produced is proportionably improved, 

 by placing across the board in front of the pictures, a parapet 

 covered with black velvet, as high as the bottom of the pic- 

 tures, and at such distance from them as to allow the stray 

 rays from the front light to fall behind it ; and by covering 

 the whole of the upper surface of the board, in front of the 

 parapet, with black velvet, removing the check-pins to the side 

 of the board. 



G. T. 



Edinburgh, l7fA ^2^Wn 843. 



Some Remarks on the Methods in common use of obtaining the 

 Mean Temperature of Places^ and on the supposed difference 

 between the Temperature of the Air and that of the Earth, By 

 Professor VV. M. Carpenter. 



It is stated by Humboldt and others, that the mean tem- 

 perature of the coldest springs in warm climates, is often lower 

 than that of the air of the same places. If we examine those 

 agencies in which atmospheric temperature originates, and by 

 which terrestrial temperature is modified, we shall perceive 

 that such a condition could not exist, and consequently, that 

 the observations on which such conclusions were based, were 

 not accurate, or that some unsuspected agency must modify 

 the relations which should otherwise be constant. In examin- 

 ing the meteorological records of our own country and of other 

 parts, and comparing the observations made by different per- 

 sons resident at the same places, we shall perceive that the re- 



♦ Read before the Royal Scottish Society of Arts 8th May 1843. 



