SECTION VI. 



GLASS. 



1. EXPERIMENTS which have hitherto been made, in regard to 

 the physical properties of glass as a transparent medium, have 

 been conducted, generally, on purely chemical principles, and 

 mostly without reference to observed facts, as regards the growth 

 of plants, excepting, perhaps, those of the most common and 

 obvious character. Partly for this reason, and partly from care- 

 less negligence, hot-houses have long been, and still continue 

 to be, glazed with material of a very inferior description. If 

 any one doubts this, let him look at some of the finest hot- 

 houses in the country, and he will easily perceive the truth of 

 this statement ; the sickly and scorched appearance of the 

 plants under its influence, being far more painful than agreeable 

 to the eye of any one who takes an interest in the vegetable 

 kingdom. This evil, alone, renders the very best cultivation of 

 no avail. 



The most elaborate and practically useful investigations that 

 have yftt been made, in this department, are those lately under- 

 taken, with the view of securing the very best material that 

 science and art could produce, for the glazing of the great Palm- 

 house at Kew. We cannot do better than present our readers 

 with the following extract from Mr. Hunt's report to the com- 

 mittee, which we take from Silliman's Journal of Science and 

 Art, vol. iv., p. 431. 



" It has been found that plants growing in stove-houses, often 

 suffer from the scorching influence of the solar rays, and great 

 expense is frequently incurred, in fixing blinds, to cut off this 

 destructive calorific influence. From the enormous size of the 

 new Palm-house, at Kew, it would be almost impracticable to 

 adopt any system of shades that would be effective, this building 

 being 363 feet in length, 100 feet wide, and 63 feet high. It 



