ON THE KEW OBSERVATORY. 365 



Woolwich standard, was at 578*1 div., and its freezing-point at very nearly 

 92'1 div., and that the barometer reading, reduced to 32°, was 30*093 inches, 

 and the temperature of the room about 55°. 



In June considerable progress had been made in calibring, graduating, 

 &c. thermometers as standards ; some tubes having been selected with great 

 care for this purpose, and about six complete standard instruments have been 

 made. 



Hygrometers, ^c. 



On September 18, 1850, experiments had been made for testing the 

 Saussure eight-haired hygrometer*. It had been placed in a receiver, first 

 with chloride of calcium and then with water. After several trials and ad- 

 justments of the instrument, the result was that " dryness" corresponded to 

 — 5 degrees of the scale, and "humidity" to 105, the temperature during the 

 experiment being about 62°. 



In this month arrangements weje made for some experiments on tension 

 of vapour, according to Mr. Broun's method. A little apparatus was after- 

 wards constructed and some progress made. 



On the 18th, Captain Ludlow presented to us the Hygrometer and aspira- 

 tor of M. Regnaultf in their original forms, and made some satisfactory com- 

 parisons with the former and the Daniel; they corresponded to about 0°*2. 



On October 11, Colonel Sykes went over a series of observations with 

 Mr. Welsh of the wet and dry bulbs, and the (above-mentioned) Regnault 

 hygrometer, and suggested a form of record for the hygrometric observa- 

 tions, and the use of one standard dry thermometer for those observations. 



At about this time, and subsequently in examining and using this Regnault 

 hygrometer and its aspirator, it was observed that at low temperatures an 

 obstruction occasioned by the position of the cork would prevent the con- 

 venient reading of the immersed thermometer ; that the cistern, composed of 

 glass, united to metal by cement, was very apt to become leaky (in conse- 

 quence of the great variation of temperature to which they are often sub- 

 jected) ; that no trifling waste of aether was occasioned by decantinor this 

 expensive material from one vessel to another at each period of observation ; 

 that no line of demarcation (as in the Daniel) assisted the precise observation 

 of the dew-point moment ; and that the aspirator required to be refilled with 

 water, at, sometimes, a very unseasonable moment, and always with waste of 

 time, &c. 



On November 15, drawings illustrating a proposal for methods of ob- 

 viating these inconveniences, &c. were made and submitted to Colonel Sykes's 

 consideration, and his approval was the inducement for giving instructions 

 (on November 2(5) for constructing a new instrument. 



It arrived at the end of February, and early in March, having been found 

 to answer the intended purposes well in most respects, was brought into use. 

 Subsequently various little ameliorations have taken place which have brought 

 it to the state already described |. 



On October 25, a drawing of the parapet in front of the door of the North 

 Hall was made for the guidance of M. Regnault in constructing his dew-point 

 apparatus for Kew. 



On Jan. 14, Mr. Welsh made a full description and diagram of his hy- 

 grometric sliding rule. 



* Vide p. 343, ante. f P. 343, ante. 



t P. 343, ante. An apparatus of the kind has been also made by Gary for St. Mary's 

 Hospital by Dr. Ansel's desire, and others are to be made for Professor Forbes, Mr. DLxon, 

 and other gentlemen. 



