506 



SCIENTIFIC RECORD FOR 1883. 



with the gradients on the morning weather-maps of the London Meteor- 

 ological Office, as shown in the following table : 



Relative velocities for the same gradient. 



October, November, December 12.5 miles per hour. 



January, February, March 14.8 miles per hour. 



April, May, June 17.2 miles per hour. 



July, August, September 12.6 miles per hour. 



The year 15.7 miles per hour. 



The increase of velocity in April, May, and June, Buchan explains as 

 due to the fact that the wind blows over a surface warmer than itself. 

 The variations are precisely parallel to the diurnal velocity of the wind 

 where also the greatest velocity occurs when the air blows over sur- 

 faces warmer than itself, "and the ascensional movement of the air 

 tends to counteract the effect of friction and viscosity between the low- 

 ermost stratum of the air and the ground. At night-time there is a 

 deep descensional movement, and the friction between the wind and 

 the surface of the earth is thereby increased." It would seem that Bu- 

 chan has here joined together as cause and effect phenomena that are 

 only very indirectly related to each other. We have little or nothing 

 to substantiate the idea that gaseous friction and viscosity diminish 

 sensibly with rising temperature. It would seem much simpler to 

 adopt at once the rigorous demonstration and clear explanation of 

 these two phenomena given by Ferrel and Koppen. 



J. A. Plumandon, adjoint meteorologist at the observatory of Puy- 

 de-D6me, has published an excellent popular work on the prediction 



