80 



NEGRETTI AND ZAMBRA, HOLBOEN YIADUCT, B.C., 



FiG. 92. 



104. Beckley's Thermograph and Eecording Hygrometer.^ As 

 recommended by the Meteorological Committee of the Boyal Society for pro- 

 ducing Photographic records of the variations of temperature and moisture 

 in the atmosphere. 



In the engraving (fig 92) the Wet and Dry Bulb Thermometers are shown at 

 W and T. freely exposed to the external atmosphere, at H is a screw for adjusting 

 these Thermometers ; C is an accurate clock for rotating the cylinder D (upon 

 which is stretched the sensitised photographic paper) once in 48 hours ; G G 

 are gas lamps, the rays of light from them being concentrated by two condensers, 

 E E, upon reflectors M M and thence projected by the Photographic Combination 

 Lenses P P, through perforated screens and the air bubbles in the tubes of the 

 Thermometers upon the prepared paper. Upon the drum D the movements of 

 the air bubble in both tubes are hereby recorded with precision, a screen in 

 connection with the clock movement is arranged to intercept the light for 4 

 minutes every two hours, this producing white lines (time spaces) upon the 

 paper when the record is developed. 



The room in which the Thermograph is placed should be most carefully 

 darkened when the apparatus is in action. 



Price, 125, complete with two Standard Thermometers, two Bent Thermometers, 

 Clock Movement, Sec., fyc.. complete, made to order. 



