4 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 93 



solid packing of wood, leaving a space 10 by 17 inches in cross-section, 

 where a speed up to 60 feet per second was obtained, as measured by a 

 water gage. 



The balance consisted of two uprights, pivoted at the base and con- 

 nected by a horizontal wire at the top. This passed through eyes on 

 two stiff wires attached to the leading edge of the testing surface. Drag 

 was measured by weights in a scalepan, attached to the model mounting 

 by a string running over a pulley, and lift was measured by a weight, 

 suspended under the testing surface at the supposed center of pressure. 

 The balance was pushed into the tunnel where the current was swiftest, 

 so that the scalepan was outside the tunnel, and the suspended weight 

 in a hole in the wood packing." 



Fig. 2. — Phillips' balance. 



While Wenham studied planes only, Phillips turned his attention to 

 curved surfaces. His were the first systematic studies of cambered air- 

 foils, a subject about which practically nothing was known before. 

 Phillips noticed the partial vacuum above the airfoils. He patented a 

 number of profiles, and introduced the downward curving leading edge, 

 now in almost universal use. Several of the airfoils developed by 

 Phillips had a maximum lift-to-drag ratio of about 10, an efficiency 

 adequate for pioneer flying and not known to have been surpassed 

 before the arrival of modern wind tunnels." 



The " Venetian blind " airplane built by Phillips, on the basis of data 

 obtained in his wind tunnel, readily lifted itself in tethered flight, and 

 was, with its cambered surfaces, a distinct improvement over its 

 predecessors. 



LUDWIG MACH 



Dr. Ludwig Mach of Vienna in 1893 was the first to use a wind 

 tunnel to photograph the flow of air. The tunnel had a cross section 

 of 18 by 25 centimeters ; one side was of glass and the others black on 

 the inside. The air was sucked through by means of a centrifugal fan 



■* Engineering, vol. 40, pp. 160-161, illus., London, Aug. 14, li 

 * British Patent, no. 13,768, 1884; and no. 13,311, 1891. 



