TRANSACTIONS OF SKCTIO.V 0. 869 



rams have beeu alreadj employed, and the author expects to employ even greater 

 velocities in future. 



The great aid supplied by these macliines to the problem of transmission of 

 power is then pointed out. The incidental advantages of using compressed air for 

 this purpose ore great, but the practical objection hitherto has been the loss of 

 power incurred in compressing air. As this loss is by the use of the above 

 method almost entirely eliminated, this method of transmitthig power will, it is 

 believed, compare favourably with any known method. The reason for the very 

 great ethciency obtained in compressing air (besides simplicity of the apparatus) 

 is that it is accomplished with hardly any heating, because the air during com- 

 pression (1) is surrounded by and is in contact with cold water in very large 

 quantities; (2) is compressed in a chamber which is washed inside and out a: 

 every stroke by large quantities of cold water ; and (3) metal surfaces similarly 

 cooled can be added in the midst of the air to any desired extent. 



5. On a Neiv Furm of Windmill. By Professoi- James Bltth, M.A., 

 Glasgow and West of Scotland Technical College. 



At the York meeting of the British Association Sir "William Thomson sug- 

 gested the construction of cheap windmills to run dynamos for charging accumu- 

 lators ; but, as i'ar as I know, no practical triiil was made till the summer of 1887, 

 when I erected my first electric windmill in the village of Marykirk in Kincardine- 

 «bire. At that time I procured a set of thirteen accumulators, and constructed a 

 windmill of the old English type, having four arms or whips and canvas sails. I 

 also tried various forms of wind-wheel of the American type, and all these I found 

 to answer very well so long as the wind had a moderate speed, but, like all other 

 experimenters with windmills, I soon found that they had either to be made self- 

 reefing or stopped altogether when a breeze came. This is obviously very unsatis- 

 factory, as the best of the wind for storage purposes is lost ; and hence this 

 problem presented itself — how to construct a windmill that would satisfy the 

 following requisites : — 



1. It must be always ready to go. 



2. It must go without attendance for lengthened periods. 



a. It must go through the wildest gale, and be able to take full advantage of it. 

 A possible solution of the problem is presented in the liobinson Anemometer, 

 which consists of lour hemispherical cups attached to four arms and moving in a 

 horizontal plane about a vertical axis. From the theory of this instrument, which 

 is only, however, approximate, it appears that, whatever may be the speed of the 

 wind, the speed of the cups attained a certain terminal value, and that the 

 couple due to the wind-pressure was exactly equal to that produced by the resistance 

 of tbe motion through the air and the friction on the bearing. It immediately 

 follows that a large machine made on this principle is likely to have the same 

 property, and hence could be allowed to run without danger even in the strongest 

 breeze, and when doing no work. 



Last summer I erected a machine of this kind, which has been considerably 

 improved within the past three months. The cups are replaced by semi-cylindrical 

 boxes attached to four strong arms, each about 20 feet long. Two boxes are placed 

 on each arm with a narrow gap between. The diameter of the outer box is 6 

 feet and its height 10 feet, while the diameter of the inner box is 3 feet, 

 and its height 10 feet. The arms are fixed in metal sockets, which are 

 attached to a strong vertical shaft made of round iron five inches in diameter.^ 

 The lower end of the shaft carries a massive pit wheel which actuates a train of 

 gearing, and drives a fly-wheel 6 feet in diameter with the requisite speed for a 

 dynamo, connected with it by a belt in the ordinary way. This machine works 

 very satisfactorily, and is at present being used to charge thirteen new E. P. S. cells. 

 With a good wind I reckon that it gives about four horse-power. I have also 

 tested it in a strong gale by allowing it to run with no load, and the result was 

 perfectly satisfactory, as a safe terminal speed was attained and all racing avoided. 



