526 proceedings: entomological society 



ammoniating and overdevelopment should be avoided. They should 

 also be kept cool. If the plates are used immediately after drying, 

 greater increase in sensitivity can be obtained by omitting the alcohol 

 from the bath and using 3V2 cc. ammonia to 100 cc. of water. 



Discussion: This paper was also illustrated by lantern slides and 

 was discussed by Messrs. Sosman, White, Humphreys and Miss 

 Kleinschmidt. 



H. S. Boyd and C. G. Peters: The calibration of precision end 

 gages. The paper was presented by Mr. Boyd. Precision end stand- 

 ards or gages, which are blocks of hardened steel or of other materials 

 made with two opposite faces plane, parallel and a specified distance 

 apart, are used as master gages for precise mechanical work. The 

 fact that these gages are made so nearly perfect that it is impossible 

 to determine their errors with any contact micrometric instrument has 

 necessitated the use of interference apparatus and methods for their 

 calibration. With these methods, developed at the Bureau of Stand- 

 ards, the above mentioned properties of gages can be determined with 

 an error of only a few millionths of an inch. In testing the planeness 

 of the gage surface a plane glass test plate is placed in contact with the 

 surface and illuminated with monochromatic light. The planeness of 

 the surface is determined from the shape of the interference fringes. 

 The length of the gage is obtained by comparison with the standard 

 light waves. An interferometer mirror is placed in contact with each 

 end of the gage, thus forming a Fabry and Perot interferometer. The 

 length of the gage is then determined from the number of waves of 

 known length between the two interferometer plates. When the 

 interferometer constructed in the manner just described is viewed in 

 parallel monochromatic light, the parallelism of the gage surfaces can 

 be determined from the expansion or contraction which takes place in 

 the ring system when the eye is moved perpendicular to the line of 

 sight. After gages of various sizes have been standardized other 

 gages can be calibrated by comparison with these standards. To 

 accomplish this a standard and an unknown gage are placed in con- 

 tact with a plane plate of glass. Another plane plate of glass placed 

 over the gages is illuminated with monochromatic light to show straight 

 fringes. The diflference in the length of the two gages is determined 

 from the relative displacement of corresponding fringes. 



Discussion: The paper was illustrated by lantern slides and was 

 discussed by Messrs. White, Peters, Mueller, Sosman, Ferner, 

 TucKERMAN and L. J. Briggs. A number of gages were exhibited 



S. J. Mauchly, Recording Secretary. 

 ENTOMOLOGICAL SOCIETY OF WASHINGTON 



3 2 8th regular MEETING 



Held February 5, 1920, at the Cosmos Club, with President Walton 

 presiding, and 30 members and 3 visitors present. 



