508 Humidity suitable for Hot-houses. 



By using a common double self-registering thermometer, and, 

 in an orchideous-house, applying the water to the spirit ther- 

 mometer, you may check your under gardener as to dryness ; 

 and, on the other hand, by wetting the mercurial thermometer 

 in the succulent-house, you may check the moisture between the 

 observations. A very neat instrument for the purpose, having the 

 two thermometers mounted side by side, and a glass fountain for 

 water fixed between them (called Mason's hygrometer), is sold by 

 Cary the optician, in the Strand ; but two of the common ther- 

 mometers will answer every purpose, provided only they agree ac- 

 curately. In keeping a register of this sort, both the temperature 

 and the dew point must be noted, to be of any service. 



I trust these instructions will be sufficient, and I hope you 

 will take the matter up, especially as regards the Orchidaceee 

 and Cactaceae, which appear to be the families more immedi- 

 ately depending upon the vaporous state of the atmosphere 

 for their successful cultivation, of any of the plants requiring 

 particular management. The former are my favourites. I 

 grow a few, and, of course, look after all the information on 

 the subject that is published. Amongst other papers that have 

 passed under my notice is one by yourself, in the 2d vol. of 

 Paxton's Magazine of Botany, relative to the rearing of young 

 plants of this interesting tribe ; and I should feel obliged if 

 you would inform me whether you still continue that practice, 

 and especially (as I perceive you now receive many importations 

 at Kingsbury) whether you adopt the same mode of treatment 

 with the newly imported specimens, or, if not, what other. 

 As regards the latter, I confess I have not succeeded as well 

 as I could wish, for they have too generally damped off, or 

 rather rotted, after making a young shoot; but before it has 

 been perfected. Any hints on this subject will be acceptable ; 

 and also on the best mode of packing them for the voyage, in 

 which I observe by the Gardener's Magazine for March last 

 and this month, the collector Mr. Harris has out has been very 

 successful. 



I am aware I am causing you some trouble, but am persuaded 

 that the result of the hygrometric observations will be of essen- 

 tial service to all interested in gardening. 



'Newcastle upon Tyne, July 26. 1839. 



Our readers will find a valuable paper " On the Relations 

 of Heat, Moisture, and Evaporation, in natural and artificial 

 Atmospheres," by the late Mr. Tredgold, in our first volume. 

 The recurrence to that article reminds us of a scheme which 

 we formed at the time Mr. Tredgold sent us the paper; 

 and we have often wished that we could meet with some 

 wealthy individual who would carry it into execution. It is to 



