H. A. Hazen — Wind Velocity and Pressure. 243 



tempts were made, at first, to use a tricycle in calm weather. 

 Plates were carried on different days and at varying speeds, but 

 it was found, finally, that the resistance to be measured was so 

 small, and the apparatus so sensitive that the jarring, even on 

 the smoothest pavement, and very slight breaths of air, vitiated 

 the results, and rendered the method unsatisfactory. The same 

 may be said of experiments on a whirling machine, in the open 

 air, used in connection with the pastime " hobby horses." In 

 this case the arm of the apparatus, 12 ft. in length, was increased 

 to 17 ft. by the use of gaspipe. The pressures were measured, 

 by the elongation of a spiral spring. The plate, suspended by 

 delicate threads from an upright, was kept vertical by pulling 

 on the spring and its observed elongation indicated the pres- 

 sure exerted. In both these cases the greatest velocity attained 

 was 12 miles per hour. In the latter case the experiments were 

 interfered with by the effects of centrifugal action upon both 

 the plate and the observer. The results may be expressed by 

 the formula : 



p=-005 SV\ 



The plates ranged from 144 to 576 sq. in. area. 



Experiments were next tried in a room 14 by 25 feet, and 

 afterward, with the same apparatus enlarged, at the building of 

 the TJ. S. Fish Commission, in a room about 50 ft. sq., but giv- 

 ing only 40 ft. clear space. The details of the latter apparatus 

 will be given here. A heavy gas pipe, 34 feet in length, was 

 suspended by two ropes from a beam in the attic, a hole hav- 

 ing been cut in the ceiling of the operating room. The point 

 of suspension was just below the swivel of a chain, and the 

 ropes could be spread to any desired angle on the bar. The 

 motive power was obtained by winding up the ropes one upon 

 the other, by turning the lower part of the swivel, and the un- 

 winding produced a most excellent, uniform, and steady motion. 

 At the higher rates of speed it was found that the ropes were in 

 danger of cutting each other by the extreme tension. This was 

 obviated by inserting a rod of -f in. iron, and winding the two 

 ropes upon that. The method of measuring the resistance was 

 to allow the plates, suspended by delicate threads either 4 or 8 

 feet in length, to swing to various angles. The size of the 

 angle was measured by looking on a scale having such large 

 divisions that they could be read easily at the axis of the ap- 

 paratus. At first it was proposed that the observer should sit 

 at the centre of the bar and make readings of the scales, as he 

 faced them, at any moment, but it was found that the whole 

 apparatus, notwithstanding its weight of 350 pounds, was so 

 delicate in its adjustments that slight movements of the hand in 

 making a record were felt by the plate. It became necessary, 



