258 



it in the power of every individual possessed of standard weights to 

 verify his measures of capacity with the utmost facility. 



Description of an improved Hygrometer. By Mr. Thomas Jones. 

 Communicated by Captain Henry Kater, F.R.S. Read June 16, 

 1825. [Phil. Trans. 1826, Part II. p. 53.] 



The principle of Mr. Jones's Hygrometer is essentially the same 

 with that of Mr. Daniell's, or rather with that employed by Mr. Dai- 

 ton to determine the quantity of aqueous vapour present in the air, 

 viz. to ascertain the temperature at which dew is deposited from the 

 atmosphere. It differs from Mr. Daniell's, however, in the frigorific 

 action being applied immediately to the bulb of the thermometer em- 

 ployed to measure the temperature. 



This bulb is of a considerable size, and of a cylindrical form, slightly 

 flattened, and extended at the end. The stem of the thermometer 

 being twice bent at right angles, this end of the bulb turns upwards. 

 It is made of black glass and is exposed, but the rest of the bulb is 

 covered with muslin. This being moistened with ether, the mercury 

 is cooled, and dew at length settles on the exposed part, at which 

 moment it is read off. 



Mr. Jones, after describing this instrument, obviates an objection 

 to its use, drawn from the application of the frigorific process to the 

 lower part of the bulb, while the dew is deposited at the upper. This 

 objection, if valid, might be obviated, by inclining the bulb so as to 

 have its axis horizontal. But repeated trials have satisfied him of 

 there being no occasion for this precaution. 



Mr. Jones finally alludes to the use of a similar construction in 

 Vienna. 



Observations on the Changes which have taken place in some ancient 

 Alloys of Copper. By John Davy, M.D. F.R.S. In a Letter to 

 Sir Humphry Davy, Bart. P.R.S. Read November 17, 1825. 

 {Phil. Trans. 1826, Part II. p. 55.] 



Dr. Davy first describes the nature of an incrustation upon an an- 

 cient helmet found in a shallow part of the sea, between the citadel 

 of Corfu and the village of Castrades. The surface was of a varie- 

 gated colour, mottled with spots of green, dirty white, and red. 

 The red and green patches exhibited minute crystals of red oxide of 

 copper, and metallic copper ; and were further composed of its green 

 submuriate and carbonate. The dirty white parts consisted chiefly 

 of oxide of tin. These new combinations are only superficially pro- 

 duced ; the metal was found bright beneath, and consisted of copper 

 alloyed with 18'5 parts of tin. 



An ancient nail from a tomb in Ithaca, and a mirror from a tomb 

 at Samos, in Cephalonia, afforded nearly similar but less distinctly 

 crystalline results. The copper in the mirror was alloyed with 6 per 

 cent, of tin, and a minute portion of arsenic. 



