6 



Lieut.-General Sabine on the Results of [June 17 



atmosphere. " The most convenient mode of photographic investigation 

 and record which presented itself, and was adopted at Kew, was by the 

 employment of wet and dry thermometers; the difference between the 

 two thermometers admits of exact measurement, and supplies the element 

 which is desired, the accuracy of the record being occasionally tested by 

 comparison with the results obtained by Regnault's " hygrometre a con- 

 densation"*. The gain of even two years of observation over a single year 

 may be here at once seen by the greater regularity of the two years' record 

 at the Siberian stations. Taking these therefore in the first instance, we 

 find that at both stations the elasticity of the vapour presents a single pro- 

 gression, having maxima about noon, and minima at 16 hours (4 a.m.). 

 The difference in the amount of vapour at the two stations is due, of course, 

 to the greater altitude of Nertchinsk. At Kew the progression is not quite 

 so regular as where two years are combined ; the values at 21, 22, and 23 

 hours are high in comparison with the other hours, possibly owing to pecu- 

 liarities in the weather of the particular year ; in other respects the pro- 

 gression is similar to that at Nertchinsk and Barnaoul, and the time of 

 minimum is identical at the three stations, viz. at 16 hours. The higher 

 elasticity of the vapour at Kew, in comparison with the two Siberian 

 stations, is, of course, due to the higher temperature at Kewf. 



In the case of the Barometer there are slight indications at each of the 

 three stations of the existence of a double progression ; but in the middle 

 latitudes a longer series of observation is clearly required to determine regu- 

 lar periods (if such there are) in a satisfactory manner. One conclusion is ob- 

 vious, that in the latitudes of 51° and 53° the striking regularity and mag- 

 nitude of the double period which prevail in the tropics do not subsist. 



The minimum of the dry air coincides at the three stations, as nearly 

 as may be, with the warmest hour of the day (2 or 3 hours). There is 

 also, at each of the three stations, an approximate maximum at or near the 

 coldest hour. At^ Barnaoul and Nertchinsk the progression between the 

 hours of minimum and maximum is uninterrupted ; at Kew it is obvious 

 that a single year is not sufficient to justify conclusions in this respect. 



Regarding the Humidity^ the minimum, or dryest hour of the 24, is in 

 all cases coincident with, or closely following upon, the warmest hour ; 

 and the hour of greatest humidity that of the lowest temperature. Kew 



* There have been some few occasions in this, the first year at Kew, when the con- 

 tinuity of the trace from the wet thermometer failed, in consequence of the freezing 

 of the water by which its ball was wetted, or owing to other causes. Arrangements 

 have now been made to meet these difficulties in continuous registration. 



f The Tables employed in the calculation of the values inserted in the columns of 

 " Elastic Force of Vapour " and " Humidity" have been the well-known Russian Tables, 

 1 Tables Psychrometriques et Barometriques a l'usage des Observatoires Meteorologiques 

 de 1' Empire de Russie.' Very convenient Tables have also been published by the 

 Smithsonian Institution, computed by Dr. Guyot. Two of the three stations of the 

 present paper being Russian, it was deemed advisable to employ the Russian ' Tables 

 Psychrometriques, &c.' for the reduction of the results in the present paper. 



