342 REPORT — 1851. 



is about 5 feet. The height of the base (a') from the grass below the steps 

 is about 11 feet, and from the stone platform 3 feet 9 inches. 



A is a wooden painted frame 2 feet 6 inches square. 



a', a base-board attached to the lower part of A, &c. 



a"^, the underside of a strong piece (represented by dotted lines) attached 

 to the upper part of A, &c. 



a^, an interior portion of a penthouse composed of very thin boards at- 

 tached to a ' and a^. 



a*, a similar exterior part of the roof, nailed to three narrow fillets, which 

 are also attached to a^, and maintain an interval of about an inch between a' 

 and a* ; thus allowing a free circulation of air between them. 



a", the remaining part of the roof. 



a^ and a^, rails ; the former adjustable for height above the latter. 



B is a strong spar or post, firmly attached by wedges, &c. to the balustrade; 

 in its upper end is fixed a cylindrical pin, which freely enters a socket in the 

 central part of a^, and allows A, with all its adjuncts, to be revolved on the 

 axis of B. 



The Dry Standard Thermometer, C, by Newman, has a brass Fahrenheit 

 scale divided to 0*5 inch. It was found on September 21, 1850, to read 

 22° in pounded ice*. 



A Dry Thermometer, D, by Ronchetti, has an ivory Fahrenheit scale di- 

 vided to 0*2 inch. The tube and scale are enclosed in a hermetically sealed 

 thin glass tube. The index corrections, when it was compared with C (on 

 September 21, 1850), were at 32° — 0-1, at 54°-|-0'2, at 73° + 0-5. 



A Wet-bulb Thermometer, E, by Ronchetti, is exactly similar (in form, &c.) 

 to D. The coating of its bulb is of taffetas, and the conducting threads are 

 of floss silk. Its index corrections, when it was compared as above, were, at 

 32° — 0-5, at 54° — 0-2, at 73° 0-0 



c' is a glass fountain whick supplies the water. It is mounted on an ad- 

 iustable support. 



The Mason's Hygrometer, by Newman, was attached to the stand at about 

 the place of E until September 22, 1850. Its index corrections, when it 

 was compared with C, as above, were at 32° 0-0, at 54°— 0-1, at 73°— 0-5. 



The Rutherford Maximum and Minimum Thermometers, FF, by Newman, 

 have boxwood scales, the minimum divided to 0'067, the maximum to 0'047 

 inch. The index corrections (as above found) for the maximum were, at 

 32°— 1°-5, at 54°— 9°-2, at,73°— 2°'0, and for the minimum at 32°— 0-3, at 

 54°— 0-4t. 



* Since the above was written comparisons of this thermometer with standards, made 

 here, gave the following results : — 



Readings of Newman's. Error of Newman's. 



32 0-00 



43-5 +0-21 • 



53-6 +0-42 



62-2 +0-52 



71-7 +0-54 



81-7 +0-55 



86-6 +0-58 



t It is evident that these instruments attached to the stand may be always protected from 



