Iviii REPORT — 1867. 



(B) "Work done at Kew as the Centeai Obseetatoet op the 

 Meteorological Committee, 



Mr. Stewart, as Director of the Central Meteorological Observatory, having 

 been called ixpou to arrange the self-recording instruments required by the 

 Meteorological Committee, has obtained the cooperation of Mr. Becklcy, me- 

 chanical assistant at Kew, from whom he has derived very great aid, and in 

 conjunction with him has arranged the Self-recording Thermograph and 

 Barograph which have been adopted by the Meteorological Committee. 



The following are the chief characteristics of these instruments : — 



Tliermogmpli. — In this instrument an air-speck, formed by a break in the 

 mercurial column of a thermometer, allows the light of a gas-lamp to pass 

 through it, yielding an image that is obtained on a revolving cylinder covered 

 with photographic paper. 



As the cylinder revolves once in forty-eight hoiu's, and as the thermometric 

 column rises and falls, these motions delineate a curve, by means of which 

 the temperature of the thermometer is denoted from moment to moment. 

 There would bo but one curve if there were only one thermometer ; in 

 practice there are two, the dry and wet bulb, the object of the first being 

 to register the temperature of the air, and of the second to register that 

 of evaporation. In this Thermograph the simultaneous records of these two 

 thermometers are obtained, the one under the other, on the same sheet of 

 paper. We have thus an under curve denoting the readings of the wet-bulb 

 thermometer, and a curve above it denoting those of the dry-bixlb thermo- 

 meter. 



An arrangement connected with the clock of this instrument has been 

 proposed and executed by Mr. Beckley, by means of which the light is cut 

 olf from the sensitive paper for foiu' minutes every two houi'S. A small 

 break is thus produced every two hours on each curve, by means of which 

 the time of any phenomenon may be easily ascertained. By drawing lines 

 through the simultaneous breaks of the wet and dry-bulb ciu'ves, a series 

 of lines is obtained perpendicular to the direction of motion of the cylinder, 

 which serves the purposes of a zero-line. Lastly, a Kew Standard Ther- 

 mometer, similar in size and figure to those of the Thermograph, and placed 

 between them (outside the house), is used as the standard of reference, and, 

 as such, is read (by eye) five or six times a day. By this means an independent 

 determination of the temperature of the air may bo obtained from time to 

 time. 



The Thermograph has been for some time ready to commence continuous 

 registration. Hitherto this has been delayed with the view of making ex- 

 periments designed to improve the working of the instrimient, because uj) to 

 the present time these improvements could be easily adapted to the other 

 instruments in course of construction. It is intended to commence the regular 

 working of the instrument before the beginning of September. 



Barograph. — The arrangement for cutting ofl^ the light every two hours, and 

 the precaiition of comparing the observations with those of a standard instru- 

 ment, read five or six times a day, will be introduced in the Barograph as 

 well as in the Thermograph. The correction of the Barograph for tempe- 

 rature is the only thing to which it is necessary to allude. Here the curve 

 denotes an uncorrected Barometer : the zero-line is not a straight line, but 

 is formed by the interception of the light from the cylinder by a stop which, 

 by means of a lever arrangement, rises and falls with temperature as much 

 as the barometric column rises and falls from the same cause ; that is to 



