THE ARTIFICIAL SEASONINCx OF TIMBER 



409 



The wet and dry bulb mcrcur}-' thermometers arc therefore the basis 

 of all readings. These, however, in the ordinary form, have to be 

 observed frequently, and the readings noted down. In order to keep a 

 continuous and autographic record of the conditions in the dryer, the 

 recording wet and dry bulb hygrometer is used. This instrument is 



Recording Hygrometer (also Thermometer) as placed in Erith Dryer. 



Recording Hygrometer in Sturtevant Dryer, 



made in two forms, similar in general principles, but diflering as to the 

 form of chart used. The one type carries the paper on a circular dial, 

 and is Umited to a certain number of days per chart (generally 7 days), 

 and the other winds up the paper on to a drum, and can take charts of 

 considerable length, the unused part being wound on a spool. 



The dial or the drum is moved by clockwork, and the expansion or 



