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February 16, 1860. 

 Sir BENJAMIN C. BRODIE, Bart., President, in the Chair. 



The following communications were read : 



I. "Description of an Instrument combining in one a Maxi- 

 mum and Minimum Mercurial Thermometer, invented by 

 Mr. JAMES HICKS." By BALFOUR STEWART, Esq. Com- 

 municated by J. P. GASSIOT, Esq. Received Feb. 7, 1860. 



About a fortnight since, Mr. James Hicks, the intelligent foreman 

 of Mr. L. P. Casella, Optician, called at Kew Observatory with an 

 instrument of the above description, for the purpose of having it 

 compared with the ordinary maximum and minimum thermometers. 

 This comparison proving very satisfactory, and the principle of the 

 instrument commending itself to Dr. Robinson, Mr. Gassiot, Pro- 

 fessor Walker, and several other scientific men who examined it, 

 Mr. Gassiot requested me to write a short description of it, whinh 

 he thought might be of interest to tbe Royal Society. For many 

 particulars of this description, I am indebted to Mr. Casella and 

 Mr. Hicks, who furnished me with details regarding the construction 

 of the instrument. 



Its chief advantage consists in its furnishing us with a mercurial 

 minimum thermometer, no serviceable instrument of this description 

 having hitherto been made. At the same time it is also capable of 

 being used as a mercurial maximum thermometer. 



The principle of the instrument is briefly as follows : 



It has a cylindrical bulb nearly 3^ inches long and half an inch in 

 diameter, filled with mercury. This gives a bore nearly -^th of an inch 

 wide, and a scale on which 1 Fahr. corresponds to about -^th of 

 an inch. "When the graduation has reached 150 Fahr. or so, both 

 the tube and the scale are made to assume a position at right angles 

 to that which they occupied previously, so that the first portion of 

 the thermometer being vertical, the second will be horizontal. The 

 numbers on the horizontal scale are not, however, in continuation of 

 those on the vertical ; for in the instrument from which this account 

 is taken, while 150 is the highest division on the vertical scale, the 

 first on the horizontal is 10, the next 0, the 3rd 10, and so on. 

 The reason of this method of graduation will immediately appear. 



