18 L. CASELLA'S CATALOGUE 



" Notwithstanding the great pressure to which these instruments had been subjected, all of them, without 

 exception, recovered their original scale-readings as soon as the pressure was removed." 



In sea-water of sp. gr. 1.027, '^ e pressure in descending increases at the rate of 280 Ibs. upon the square 

 inch for every 100 fathoms, or exactly one ton for every 800 fathoms. 



On completing this arrangement, a few of the instruments were immediately forwarded by 

 Captain Richards from the Hydrographic Office to Dr. Carpenter and Dr. Wyvell Thompson 

 then on board Her Majesty's Ship Porcupine, Captain Calver, at that time on a voyage of deep 

 sea investigation in the North Atlantic, the results of which were shortly afterwards given to 

 the Royal Society by Dr. Carpenter (see " Proceedings of the Royal Society," 1870), and this 

 thermometer, under the name of the CASELLA.MILLER THERMOMETER was at once exclusively 

 adopted by the Government for all investigations of deep sea temperature, with the guarantee 

 of Mr. CASELLA to the authorities, that all should be subjected in his apparatus to an 

 hydraulic pressure of not less than two and a half tons to the square inch=2000 fathoms 

 depth in the sea. 



Instructions. The Six's thermometer is used vertically, and should always be kept upright 

 or with the head well raised especially in carriage. Before observation the indices should 

 be set by applying the ends of the accompanying magnet close to the glass, and drawing them 

 gently down to the surface of the mercury in each stem. On a rise of temperature, the 

 spirit will expand and depress the mercury in the left-hand stem, while it raises it in the other, 

 carrying up with it the index to whatever degree the heat may attain. A return of cold will 

 contract the spirit in the bulb, allowing the elastic force of the compressed air in the opposite 

 bulb to depress the mercury in the right-hand stem, which then rises on the opposite side, 

 raising the index in like manner to register the extreme of cold ; the indication in each case 

 is at the end nearest the mercury, whilst the mercury at each end shows the temperature of the 

 time being. The greatest heat is shown at the top of the right-hand stem, and at the bottom of 

 that on the left. 



43. The Casella-liller Deep Sea Self-Registering Thermometer, as above, protected 



in vulcanite mounting, with black divisions, etc., on glass, very legible, in 

 round copper case 7i-inch. by H-inch. outside (fig. 48) p. 16 250 



Tor other Six's Thermometers, see Kos. 203, 204, 204* 210. 



49. Babinet's Apparatus^ with two thermometers, for taking the exact temperature of 

 the air (fig. 49) p. 21 . . . 1 10 



The slow and unequal transmission of heat by air and water is well known ; the temperature 

 of a body of the latter being only obtainable by its constant agitation. The above arrangement 

 gives the same means of agitating the ambient air in order to ascertain its true temperature as 

 well as the effect of its friction on the thermometer bulb. 



HYGEOMETEES. 



50. Mason's Hygrometer (wet and dry bulb) with metal scales, mounted on mahogany 

 board for suspension. The thermometers are divided on the stem, and the 

 figures indelibly burnt in on porcelain slips at the side, as supplied by 

 L. CASELLA to the various Government Departments and the Members of the 

 British Meteorological Society (fig. 50) p. 19 . . 250 



52. MASON'S HYGEOMETEE ; like/,g-. 50, but mounted on porcelain scales 1 15 



