ERRATA. 



The key number of Messrs. Adam Hilger, Ltd., should be 

 included after the names of the following instruments : 



Absorption Apparatus. 

 Collimator. 

 Colorimeter. 

 Colour Perception Ap- 

 paratus. 

 Concave Lens. 



Mirror. 

 Direct Vision Spectro- 

 scope. 



Double Image Prism. 

 Erecting Prism. 

 Eyepiece. 



Diagonal. 



Huyghenian. 



Positive. 



Ramsden. 

 Fabry & Perot Inter- 

 ferometer. 

 Filter, Light. 

 Galvanometer Mirrors. 

 Gas Analysis Apparatus. 



Interferometer, Fabry 



& Perot. 

 Interferometer, Lum- 



mer & Gehrcke. 

 Lens, Achromatic. 

 Mica Wave Plates. 

 Micrometer Eyepiece. 



Screw. 



Mirror. 

 Nicol Prism. 

 Object Glasses. 

 Ocular. 



Optical Mirror. 

 Parabolic Mirror. 

 Photometer. 

 Polarising Apparatus. 

 Positive Eyepiece. 

 Prism, Foucault. 



NicoFs. 



Rutherford's. 



Thompson. 

 Ramsden Eyepiece. 

 Rutherford Prism. 



Schumann Plates. 



Screen, Filter. 



Solar Diagonal Eye- 

 piece. 



Spectrograph, Concave 

 Grating. 



Spectrograph, Fery. 



Spectrograph, Quartz, 

 Arc Form. 



Spectrograph, Quartz, 

 Littrow. 



Spectroscope, Direct 

 Vision. 



Spectroscope, Evershed. 



Spherometer. 



Strain-Measurer. 



Telespectroscope. 



Tension Meter. 



Tetragonal Prism. 



Thermo-couple. 



Thermopile. 



Viscometer. 



The address of the British Optical Instrument Manufacturers 

 Association should read : 



Duke Street, London, S.W.i. 



