356 SCIENCE PROGRESS 



formulated by Miss Cannon and which is now universally 

 accepted, having been unanimously adopted by the Inter- 

 national Committee appointed by the Solar Union. It is 

 described in full in H.A. 28, and more concisely in H.A. 56. 

 Over 2,100 plates were examined and 242,093 spectra were 

 classified. The results are to be published in nine volumes, 

 of which the first was referred to above. The revision and 

 preparation of copy for press has occupied two years, and the 

 publication of the remaining volumes will cover a further period 

 of two years. As showing the care with which the work has 

 been carried out, the following extract from the preface is of 

 interest : "To secure the greatest efficiency, it was evidently 

 necessary to employ the methods of scientific management. A 

 loss of one minute in the reduction of each estimate would 

 delay the publication of the entire work by the equivalent of 

 the time of one assistant for two years. It was therefore im- 

 portant to study with care each step in the reduction, including 

 the identification, the preparation of the card catalogue and 

 copy for the printer, the determination of the magnitudes, and 

 the checking of the entire work." 



The catalogue itself contains a vast mine of useful informa- 

 tion in addition to the spectral type. Successive columns con- 

 tain the B.D. number of the star ; its R.A. and Dec. for 1900 ; 

 and its photometric and photographic magnitudes on the 

 Harvard scale (from which its colour-index can be obtained). 

 Extensive notes give details of any peculiarities in the spectra, 

 and in the case of variable stars the designation, the type of 

 variability, the maximum and minimum magnitudes, the period 

 and (if known) the parallax are given. A reference is also made 

 to any large proper-motions. The catalogue includes stars as 

 faint as the nth magnitude, although it is not complete to 

 that faintness. 



It will readily be realised that the complete catalogue will 

 prove invaluable as a work of reference, for in practically all 

 modern investigations connected with stellar dynamics a know- 

 ledge of the types of the stars is necessary. The volumes are 

 therefore being made to stand plenty of thumbing, the paper 

 used containing 80 per cent, of rags, so that it will be 

 practically permanent. Miss Cannon is to be congratulated on 

 the successful completion of so important and vast an under- 

 taking. 



