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On the Registry of the Hourly Variations of the Thermometer, 

 by means of Photographic Papers. By MUNGO Ponton, 

 Esq., F.R.S.E., F.R.S.S.A. Communicated by the Royal 

 Scottish Society of Arts.* 



An tin exceptionable mode of registering the hourly variations 

 of the common mercurial thermometer, has long been a deside- 

 ratum in science. Hitherto we have been able to register only 

 the maximum and minimum of temperature for each day and 

 night, and even that in rather an imperfect manner ; but to re- 

 cord the hourly movements of the mercury in the thermometer 

 has not, so far as I am aware, been as yet successfully attempted. 

 Various purely mechanical methods have been tried from time 

 to time, but without satisfactory results. Nature, however, is 

 full of appliances ; and it only requires perseverance on our 

 part to avail ourselves of the implements so profusely scattered 

 around us. 



The newly discovered phenomena of photography appeared 

 to me likely to afford facilities for attaining tlie object in view ; 

 and the results I have arrived at lead me to hope, that we may 

 successfully employ light to record, with its subtile pencil, the 

 changes in the heat of the atmosphere. 



The first difficulty to be overcome was to obtain a clear and 

 well defined shadow of the filled portion of the bore of the 

 thermometer, capable of being distinguished from the shadow 

 produced by the empty portion. This is a matter of some 

 nicety. After several trials, the following appeared to be the 

 best mode of securing this result : — Select a thermometer with 

 a flat bore, and grind the stem down on one side nearly to the 

 bore, so as to produce a flat, or rather slightly concave, polished 

 surface, and let the opposite side be ground only a little flat. 

 If the latter flattened side be now exposed to the light of a 

 lamp oi" gas flame, condensed by means of a cylindrical glass 

 vessel filled with A/ater, placed at a considerable angle, it will 

 be found, that by a little nice adjustment a certain position will 

 be obtained, in which the shadow of the bore may be thrown 

 on a piece of paper placed against the other ground sui'face of 



* Read before the Society on 10th March and 12th May 1845. 



