September 30, 1921] 



SCIENCE 



291 



X-ray by Friman ' of a wave-length of 12.346 

 Angstrom units. There is thus at most a mat- 

 ter of about four octaves still to be explored. 

 In approaching this unknown region from the 

 violet end the most characteristic property of 

 the radiations appears to be their intense ab- 

 sorption by practically every kind of matter. 

 This result is not very surprising from the 

 quantum standpoint. The quantum of these 

 radiations is in excess of that which corre- 

 sponds to the ionizing potential of every known 

 molecule, but it is of the same order of magni- 

 tude. Furthermore, it is large enough to reach 

 not only the most superficial, but also a num- 

 ber of the deeper-seated electrons of the atoms. 

 There is evidence, both theoretical and experi- 

 mental, that the photoelectric absorption of 

 radiation is most intense when its quantum 

 exceeds the minimum quantum necessary to 

 eject the absorbing electron but does not ex- 

 ceed it too much. In the simplest theoretical 

 case the absorption is zero for radiations whose 

 frequencies lie below the minimum quantum, 

 rises to a maximum for a frequency compar- 

 able with the minimum, and falls off to zero 

 again at infinite frequency. This case has not 

 been realized in practise, but, broadly judged, 

 the experimental data are in harmony with it. 

 On these general grounds we should expect in- 

 tense absorption by all kinds of matter for the 

 radiation between the ultra-violet and the 

 X-ray region. 



The closeness of the similarity in the prop- 

 erties of X-rays and light is, I think, even 

 yet inadequately realized. It is not merely a 

 similarity along broad lines, but it extends 

 to a remarkable degree of detail. It is per- 

 haps most conspicuous in the domains of 

 photoelectric action and of the inverse phenom- 

 enon of the excitation of radiation or spectral 

 lines by electron impacts. Whilst there may 

 still be room for doubt as to the precise inter- 

 pretation of some of the experimental data, 

 the impression I have formed is that each im- 

 portant advance tends to unify rather than to 

 disintegrate these two important groups of 

 phenomena. 



O. W. ElCHARDSON 



■•Phil. Mag., Vol. XXXII., p. 494 (1916). 



SCIENTIFIC ABSTRACTING i 



7s it worth while for scientific journals to 

 provide abstracts at the beginning of their 

 articles? 



The answer to this question depends, of 

 course, on the nature of the abstracts. If they 

 are sketchy, incomplete and unreliable, as 

 many abstracts published at present are, they 

 may be worse than useless. But suppose each 

 abstract describes the contents of the article 

 so completely and precisely that any reader can 

 tell with assurance whether the article contains 

 any results of interest to him, and suppose it 

 summarizes the methods, conclusions and 

 theories so as to give all the information any 

 reader not a specialist in the narrow field in- 

 volved needs; that is, suppose each is the 

 result of a careful analysis of the article by a 

 competent abstractor, would not such abstracts 

 enable the reader to grasp the significant re- 

 sults in the articles not only more quickly but 

 more completely and clearly than by skim- 

 ming through the articles? 



Such abstracts would save much time for 

 the scientist not only as a reader of current 

 literature but also as an investigator. For 

 when he desires information on a certain nar- 

 row subject, such abstracts would help him to 

 determine more quickly than otherwise which 

 of the articles referred to in a bibliography or 

 other list contain what he needs; and fre- 

 quently the abstracts would give him the in- 

 formation directly and make a search through 

 the articles unnecessary. Finally, such ab- 

 stracts would save his time as an abstractor 

 at home and abroad. For abstract journals 

 are recognized to be such useful, almost in- 

 dispensable guides to scientific literature that 

 most sciences have one or more in each of the 

 great scientific languages. At present, then, 

 most of the articles in the fields of astronomy, 

 physics, chemistry, biology, and medicine are 

 abstracted from three to six times each, while 

 if an abstract suitable for reprinting in an ab- 



1 The method of analytic abstracting described 

 in this paper was developed by the writer during 

 1919-20 while on the staff of the Research In- 

 formation Service of the National Research 

 Council. 



