480 REPORT — 1881. 



In tlius accomplisliing the work of a farm from a central-power station, 

 considerable savings of plant and labour may be effected ; the engine-power 

 will be chiefly required for day work, and its night work, for the purposes 

 of electro-horticulture, will be a secondary utilisation of the establishment 

 involving little extra expense. At the same time the means are provided 

 of lighting the hall and shrubberies in the most perfect manner, and of 

 producing effects in landscape gardening that are strikingly beautiful. 



Since writing the above my attention has been called to a very 

 interesting Report entitled ' Researches on the Influence of the Solar 

 Rays on the Growth of Plants ' communicated to the Oxford Meeting of 

 the British Association in 1847, by Mr. Robert Hunt, F.R.S., towards the 

 end of which he gives the following as the conclusions arrived at. 



1. Light prevents the germination of seeds. 



2. Actinism quickens germination. 



3. Light acts to effect the decomposition of carbonic acid by the 

 growing plant. 



4. Actinism and light are essential to the formation of the colouring 

 matter of leaves. 



5. Light and actinism, independent of calorific rays, prevent the 

 development of the reproductive organs of plants. 



6. The heat-radiations corresponding with the extreme red rays of 

 the spectrum facilitate the flowering of plants and the perfecting of their 

 reproductive principles. 



On the Pressure of Wind upon a Fixed Plane Surface. 

 By Thomas Hawksley, C.E., F.R.S. 



[A communication ordered by the General Committee to be printed in extenso 



among the Reports.] 



The recent failures of the Tay Bridge and other important structures 

 during heavy gales of wind, have attracted much attention to the subject 

 of this paper. The general solution of the problem may be thus briefly 

 stated :— 



Let V = the velocity of the current in feet per second. 



h = the height through which a heavy body must fall to produce 



the velocity v. 

 w = the weight in pounds of a cubic foot of the impinging fluid 



[for atmospheric air on an average about 0"0765 Ibs.J 

 g = 32, the coefficient of gravity. 



Then li=- ^', a^^id since p, the pressure of a fluid striking a plane 



perpendicularly and then escaping at right angles to its original path, is 

 that due to twice the height h [Daubuisson's ' Hydraulics ' ; Rouse's 

 ' Experiments '] we have simply 



,1 , , • • ^ 0-0765«2 

 ^ (tor atmospheric airj 



= (^) very nearly. 



32 



