Photographic Register Thermometer. 273 



be received on the sensitive paper surrounding the inner cy- 

 linder, care being taken that the paper be applied as closely as 

 possible to the stem. 



The whole apparatus is now to be placed near a lamp, or a 

 good sized gas flame, the light from Avhich is to be concen- 

 trated on the stem by means of a cylindrical glass bottle filled 

 with water, as ah-eady described. If the registration is to be 

 half-hourly, the distance of the light may be about 2 feet ; if 

 every quarter of an hour, the distance should be about 1 foot. 



By this arrangement the image of the mercury in the bore, 

 as it stood during each half or quarter of an hour, is impressed 

 on the paper in a latent state, and the whole series may be 

 brought out at once by the sulphate of iron at the end of the 

 24 hours. 



A scale is to be adapted to the cylinder to determine the de- 

 grees, and corresponding marks should be made on the paper, 

 60 that the scale may be applied to it after removal from the 

 cylinder. A slip of paper about an inch and a half broad, 

 placed on that portion of the cylinder where the mercui-y may 

 be expected to range, will, in general, be fovmd sufficient. 



The same method of registration, although peculiarly appli- 

 cable to the thermometer, may be also employed for the regis- 

 tration of the barometer and other instruments. It has this 

 peculiar advantage, that it does not interfere in the smallest 

 degree with the natural action of the instrument, but merely 

 takes a picture of the state of the instrument during a given 

 time. The chief expense would be that of the artificial light, 

 but this might be partly economised, by a contrivance for that 

 purpose. The same artificial light might also be used for re- 

 gistering several instruments. 



The photographic paper which I have found best adapted for 

 the above purpose, is equally fitted for taking landscapes in the 

 camera obscura, because it keeps well for being taken to the 

 field, and may also be allowed to remain for so considerable a 

 time before the image is brought out. 



VOL. XXXIX. NO, LXXVIII. — OCTOBEU 1845. 



