The Rev. T. R. Robinson's Description of an improved Anemometer. 1 G9 



S. E. of it ; but it has the double disadvantage of causing additional friction by 

 the weight of the long axles, and making the whole less stable. To obviate 

 this last defect, about 3cwt. of pig ballast is disposed round the floor of H ; 

 notwithstanding which, the machine was blown down in March, 1845. After 

 this it was further secured by three iron shrouds attached to the walls in the 

 directions S. E., S.W., and N.W. ; and it has since withstood still heavier 

 gales. The axle C bears the mill G for space ; the axle D the vane V for 

 direction. 



The dimensions which I chose for the first of these are, 12 inches for the dia- 

 meter of the hemispheres, and 23 inches for the distance of their centres from that 

 of the axle. The latter might, perhaps, have been increased with advantage; but I 

 was afraid of weakening the arms too much. The hemispheres are made of sheet 

 zinc, strengthened by a wire rim ; each weighs l-311bs., but might have been 

 lighter if made of thin copper. The arms which carry them are iron, 1*.5 inches 

 broad, and 01 thick, but feathered off to a sharp edge at each side, and kept 

 from bending dowuAvards by stays of wire. The hemispheres are four ; for I 

 found, by trials with the small anemometer, that this number is better than 

 either five or three. Six is inferior to any lower number, not excepting two ; 

 probably because some eddy from the concaves reaches the convex surfaces. 

 The iron tubes T, 8 and IS^.j inches long, are secured to the diagonal of the 

 top frame, and carry boxes of bronze, in which are bronze balls, on and be- 

 tween which the axles C and D turn. This arrangement is the result of many 

 experiments. At first they turned above in common brass journals, and their 

 hardened points rested below on surfaces of hard steel. As, however, C with 

 its appendages weighs 20'691bs., and makes, on an average, 1.500 revolutions 

 per hour,* the bearing surfaces were soon abraded ; the friction also was far 

 too great, being equivalent to 104 grains acting at the centre of a hemisphere. 

 I then refashioned the pivot very carefully, and set it in an agate cup ; but, 

 though this was kept full of oil, after a year's work, I found that a hole of some 

 depth had been drilled in it. I substituted for it one of sapphire, but even this 

 failed after two years ; and the friction was not so much lessened as I expected, 



* Of this 6'69 is due to a piece of iron tube composing C, which I have recently replaced 

 by a shaft of deal; this has reduced the weight to 16-231bs. The average velocity of the wind is 

 about 10 miles per hour. 



