700 APPENDIX. 



side next the light which draws. In the top-light of frames, the want of direct 

 light at the sides may cause partly the greater elongation of the top ; but plants 

 elongate below glass, even though surrounded by light. The want of motion is 

 a great cause of this : plants uniformly elongate more in a sheltered than an 

 exposed field. If there is any such thing as attraction between light and plants, as 

 roots follow their food (which is partly hygroscopical in the latter case), it will be, 

 like the attraction of gravitation, more easily perceivable in its effects than capable 

 of explanation. Refraction will disperse the light : it is difficult to understand 

 how it should weaken what does pass through. The chemical power of light, how- 

 ever, is so much connected with electricity, that it may be weakened in a way we 

 cannot account for. The chemical power of light is greatest in the least luminous 

 part of the rays ; and yet, as the quantity of light is equal, that of the equator 

 must have most power. There is a connexion between heat, light, and electricity, 

 not yet explained ; the optical qualities of light have been much more attended 

 to than the chemical. The red rays have more momentum than the blue ; thus 

 causing the red of the rising and setting sun, and the azure blue of the sky. Per- 

 haps more of the blue or chemical portion of the sun's rays may thus be lost 

 in refraction. 



454, in p. 167. I have found the leather wallet much improved by having the 

 two sides nailed to two pieces of wood about an inch and a half wide ; and also one 

 piece down the middle, so as to form a parting ; one of which does for nails and 

 the other for shreds. H. O. 



463, in p. 173. I should think any protection from frost would be much more 

 effectual if drawn up or removed during a mild day ; the plant would be hardier 

 also and healthier, and the extremes between heat and cold not so great. In 

 Scotland, woollen nets are most used ; from the coldness of the climate they 

 are most beneficial ; and those who keep them constantly standing find they do 

 harm ; the foliage is not so healthy, and insects collect. There is seldom so 

 much heat there as to require shading for the blossom. Dry, cold east winds do 

 most harm. 



474, in p. 181. White walls will heat the air around the leaves most through 

 the day from reflection, as these are seldom close to the wall ; and the extreme of 

 cold will not be so great at night, which is most dangerous. Black-coloured walls, 

 though they absorb heat during the day, will not retain it to give off at night, as it 

 will be conducted through the wall in great part during the day, and any little 

 retained be speedily radiated off in the early part of the night. 



501, in p. 205. The temperature of the blood is 94 to 98", and the heated air 

 is not likely to be much below the temperature of the skin ; to that extent, how- 

 ever, it will undoubtedly increase the effect ; and, in motion, will give motion to 

 the leaves and stems of plants, and will not stagnate and corrupt. 



504, in p. 208. Subsequent improvements have been made on Rogers's conical 

 boiler by Mr. Shewen, and modifications of it have been adopted by Mr. Stephen- 

 son and various persons. Messrs. Garton and Jarvis, of Exeter, have invented 

 and put up at various places a boiler on the same general principle as that of Mr. 

 Rogers's, viz.. having the fire in the centre of the water but totally different in 

 mechanical construction. This boiler will be figured in the Gardeners' Magazine. 

 The boiler most generally in -use for heating horticultural structures at present, 

 is unquestionably that of Mr. Rogers as improved by Mr. Shewen. Two of 

 these are now (Oct. 1842) putting up in the Hort. Soc. Garden. 



524, in p. 225. A small building on the north side of a larger one is in a lower 



