NO. 3 



EUROPEAN AERONAUTICAL LABORATORIES ZAH M 



21 



described in the Physical Review for December, 1903, half a decade 

 before Prandtl's experiments. 



The pressure distribution over model screw propellers having 

 perforated hollow blades was measured by transmission through 

 a hollow shaft to a pressure gauge. The screws were made of co])per 

 electrically deposited on wax models, and were then emptied of the 

 wax by heating. To show the direction of air flow past the blades, 



Fig. 4. — Prandtl's Pressure-tube Anemometer 



sulphureted hydrogen was allowed to exude from perforations in 

 their surfaces, and thus to stain them. The staining streaks extend 

 fore and aft and very slightly outward radially along the screw 

 blades. 



The results of the experiments in the Gottingen laboratory have 

 been published in various German periodicals, and in part translated 

 and republished in Engineering, London, for 191 1 and 1912, all 

 of which are on file in the Smithsonian library. Particularly interest- 

 ing are Prandtl's determination of pressure distribution on models of 



