NO. 4 



PIONEER WIND TUNNELS RANDERS-PEHRSON 



at the rate of lo meters per second. A piece of wire mesh over the 

 opening served to straighten the current. By the use of silk threads, 

 cigarette smoke and glowing particles of iron, the flow could be ob- 

 served. Streams of heated air were also introduced, invisible to the 

 eye, but recording on a photographic plate. A series of good flow 

 photographs was obtained.' 



JOHAN IRMINGER AND H. C. VOGT 



The first wind tunnel measurements of pressure distribution were 

 made by Johan Irminger, and H. C. Vogt, of Copenhagen. Vogt, who 

 was a marine engineer, had made extensive studies on sails and air 

 propellers and had found that the partial vacuum on the leeward side 

 was responsible for the greater part of the thrust. Phillips was first 

 to notice a rarefaction, but did not press his investigation of this factor 

 very far. Vogt, in conjunction with Irminger, director of the Copen- 

 hagen Gas Works, undertook a series of wind-tunnel experiments to 

 establish this fact conclusively. 



Fig. 3. — Irminger and Vogt's tunnel, 1894. 



There was at the gas works a smokestack too feet high and 5 feet 

 in diameter, serving a large number of gas furnaces. In order to utilize 

 the draft in this chimney for experimental purposes, an opening was 

 made in its side and a rectangular box inserted, 40 inches long and 

 4i by 9 inches inside cross-section. The inside of the box was polished 

 and a shutter was used to control the speed of the air current, which 

 ranged from 24 to 48 feet per second. 



To determine the pressure distribution on plane surfaces, two pieces 

 of sheet iron were placed i/io inch apart, joined along the edges to 

 form a shallow closed box. To the interior of this a water gage was 



'Zeitschr. Luftschiffahrt und Phys. Atmosphare, vol. 15, pp. 129-139, pis. 

 I-III, 1806. 



