254 Mr Blackadder on Meteorological Instruments which 



very humid state of the atmosphere, ether may be requisite ; 

 but, on most occasions, rain-water is sufficient ; the use, how- 

 ever, of common ardent spirits for such a purpose, is attended 

 with but a trifling expence, and may be found convenient. 



Having thus shown how the temperature of the air and 

 other bodies may be determined, during absence, and at any 

 given instant, it may readily be conceived, how it may, in like 

 manner, be determined at successive intervals of time, by mul- 

 tiplication, and a proper arrangement of the same means. 

 Thus, seven thermometers of the before mentioned construc- 

 tion, connected by a vexy simple piece of mechanism, will 

 enable us to determine the exact temperature every hour 

 during the whole course of the day and night, and that with 

 very little trouble. For, to obtain this, it is necessary to in- 

 spect the instrument only three times in the course of the day, 

 or during that period not usually appropriated to sleep ; for 

 example, at 7 a. m., 4 p. m., and 11 p. m. 



Having described Mr Blackadder's method of registering 

 the indications of the thermometer at any given instant, and 

 at successive intervals of time, the application of the same 

 principle to the registering of the Hygrometer will not re- 

 quire much illustration : For, if it be admitted that the at- 

 mizomic hygrometer (that is, a hygrometer constructed on 

 the Huttonian principle,) may be depended upon, all that is 

 requisite to procure an accurate register is, to attach two 

 thermometers to one slip of metal, on which is engraved a 

 scale for each, and to keep one of the bulbs moist with water. 

 When at any instant the instrument thus constructed is 

 brought into the horizontal position, the index in the one 

 tube will indicate the temperature of the air, and that in the 

 other the temperature produced by evaporation. Nothing is 

 more simple than this modification of the registering appara- 

 tus, for nothing can be more easily effected than keeping one 

 of the bulbs moist with water, and in this only does it differ 

 from that fitted to register the atmospheric temperature alone. 



Hitherto there has been no method devised for registering 

 even the extremes of the barometric changes, which does not 

 infer a very considerable increase of mechanical friction ; and 

 which, consequently, does not include a degree of inaccuracy 



