The Percy Sladen Memorial Expedition to the Orange Biver. 23 



at about 2h feet from the ground. Wherever possible the bush 

 chosen was a leafless Euphorbia ; in all other cases the bushes 

 were microphyllous. The highest minimum recorded was 88° — at 

 Windhoek on the night of November 30th. This was due to a hot 

 wind blowing with much force from the top of the Giftberg, the 

 prevalence of which is indicated by the name Windhoek. The 

 thermometers used were all standardised at Kew. One of them 

 was kindly lent for the purposes of the expedition by Mr. C. M. 

 Stewart, B.Sc, Secretary to the Meteorological Commission, Cape 

 Town. 



The wet and dry bulb readings were obtained from two ordinary 

 thermometers mounted together in a metal case — the only form 

 obtainable that was likely to withstand the vicissitudes of wagon - 

 travelling. Except where it is otherwise stated, the readings 

 were taken at 2 p.m. ; those marked :;: were recorded when the 

 instrument was hung for a special purpose in a bush of Euphorbia 

 Dregeana or Mesembryanthemum Barklyi. As far as possible they 

 were shaded, but they could not be entirely protected ; this, 

 together with the reflection from the bare ground, makes the 

 readings higher than would have been given in a screen. All 

 other readings were taken under the same conditions as those 

 described for the maximum thermometer. 



The aneroid used was one of Messrs. Cary's (No. 1359). On the 

 return of the expedition it was calibrated in the physics laboratory 

 of the South African College by my colleague, Mr. W. H. Logeman. 

 The altitude readings in column 3 are obtained by applying the 

 mean of pressure corrections for rising and falling pressure, 

 assuming that pressure at sea-level = 3O07 inches, i.e., the mean 

 of the last 10 years. At the same time the results of the calibra- 

 tion were such as to lead to the conclusion that very little faith can 

 be placed in the figures obtained. 



