Heat, Moisture, and Evaporation. 37 



the end of November, when 1 reduce it to temperate, and so 

 keep it till I have cut all the grapes. This in some years is 

 the beginning, and some years the end of March. The Poo- 

 nah grape I keep till April, with the leaves on as if in sum- 

 mer. 



The wood of West's St. Peter is round, of a brown colour, 

 short jointed, eyes prominent, leaves rather small, and flat, 

 smooth, and shining underneath, deeply serrated ; they turn 

 to a purple colour as the fruit becomes black. The vine grows 

 freely, and is a great bearer ; the bunches at first showing are 

 small, and apparently weak, but gradually advance until they 

 become long with large shoulders. The blossom sets freely, 

 the berries are round, and grow of an even size, and if well 

 thinned they soon become large. When ripe, the grape is of a 

 very black colour, the skin thin, with small seeds, very juicy, 

 and high flavoured. 



There is another St. Peter grape which is known to most 

 experienced gardeners, but is very different from the one 

 above mentioned ; the leaves of this old variety are very downy 

 or woolly underneath, the edges turn downward, the berries 

 are oval, and the wood long-jointed, that is, with great dis- 

 tances between the buds. 



Spring Grove, 5th December, 1825. 



Art. XI. On the Relations of Heat, Moisture, and Eva- 

 poration in Natural and Artificial Atmospheres. By Thomas 

 Tredgold, Esq., Civil Engineer. 



The constitution of the atmosphere has a most important 

 influence on the growth of plants, and particularly its rela- 

 tion to moisture. Till within these few years the variable 

 state of the moisture in the air was not registered with any 

 degree of accuracy; and, chiefly, from the want of proper 

 instruments. A variety of contrivances have been, from time 

 to time, invented for ascertaining the quantity of moisture in 

 the air, but none of them are so perfect as it is desirable to 

 render them. The well-known expansion and contraction of 

 both vegetable and animal substances, by the effect of moisture, 

 has been tried in several ways ; but since there is no probabi- 

 lity that the change of bulk is exactly proportional to the 

 change in the quantity of moisture, these methods are not in 

 much esteem. The increase and decrease of weight from 

 moisture is objectionable for the same reason. 



There are two methods, however, which give accurate re- 

 sults, though they are not quite so easilv applied as the principle 



d3 



