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Scimtijic Intelligence. [No. 8, new series. 



3. A thermometer exposed to the sun with white bulb. It had 

 no brass scale, and a very thin capillary tube for the mercury, sur- 

 rounded by a larger glass tube, the ordinary from of thermometers 

 on the Continent. This has the advantage, that the instrument 



w jth near iy no error the temperature of 

 the mercury in the * * * * * * undisturbed by the * * 

 * * influence of appendices.) But even in this shape a thermo- 

 meter offers no absolute measure for insolation, the whiteness of 

 the glass forming the bulb, its color and transparency modifies 

 very appreciably the apparent action of the sun on different in- 

 struments. ^ 



4. A thermometer of a similar construction, with blackened 

 bulb. 



5. A Kew standard thermometer, with thick glass tube and a 

 division being in the glass stem. It had its bulb blackened, and 

 also half of the mantle of the cylinder behind the division. This, 

 as well as the following, was placed on a large surface of black 

 wood, which getting heated all round, very nearly as much as the 

 thermometer itself, prevents it from irregular loss of heat towards 

 objects of different temperature in its vicinity; for instance the 

 presence of grass or gravel, &c, would otherwise affect the height 

 of the thermometer. It may be considered as a good proof of the 

 comparability of the thermometers in such an arrangement, that 

 the Kew standard and the following thermometer, No. 6, stood 

 very nearly alike. 



6. A boiling thermometer, every degree divided in T '^, the 

 mercury begins to reach the divided scale only at 78 degrees C. 

 being intercepted by a second •enlargement of the bulb. Bulb 

 blackened. The mercury contained in the capillary tube being 

 here only a very small part of the mercury under the black stra- 

 tum, and being protected besides by a second outer glass cylinder 

 against loss of heat, I found this instrument the best for these ex- 

 periments as long as the insolation is hot enough to keep it on the 



* For relative determinations for distance, for raising the annual and 

 daily variations, careful observations with any thermometer can be 

 very useful. 



