From these two different types of connections it appears that the cita-tion network shows the existence of two different literature practices and of two different needs on the part of the scientist. (i) The research front builds on recent work, and the network be-comes very tight. To cope with this, the scientist (particularly, I presume, in physics and molecular biolohgy) needs an alerting service that will keep him posted, probably by citation indexing, on the work of his peers and colleagues. (ii) The random scattering of Fig. 6 corresponds to a drawing upon the tottality of previous work. In a sense, this is the portion of the network that treats each published item as if it were truly part of the eternal record of human knowledge. In subject fields that have been dominated by this second attitude, the traditional procedure has been to systematize the added knowl-edge from time to time in book form, topic by topic, or to make use of a system of classification optimistically considered ‘more or less eternal, as in taxonomy and chemistry. If such classi-fication holds over reasonably long pe-riods, one may have an okbjective means of reducing the world total of knowl-edge to fairly small parcels in which the items are found to be in one-to-one correspondence with some natural order.

The present research suggests that most papers, through citations, are knit together rather tightly. The total research front of science, however, has never been a single row of knitting. It is, instead, divided by dropped stiches into quite small segments and strips. From a study of the citations of journals by journals I come to the conclusion that most of these strips correspond to’ the work of, at most, a few hundred men at any one time. Such strips represent objectively defined subjects whose description may vary materially from year to year but which remain otherwise an intellectual whole. If one would work out the nature of such strips, it might lead to a method of delineating the topography of current scientific literature. With such a topography established, one could perhaps indicate the overlap and relative importance of journals and, indeed, of countries, authors, or individual papers by the place they occupied within the map, and by their degree of strategic centralness within a given strip. Journal citations provide the most readily available data for a. test of such methods. From a preliminary and very rough analysis of these data I am tempted to conclude. that a very large fraction of the alleged 35,000 journals now current must be reckoned as merely a distant background noise, and as very far from central or strategic in any of then knitted strips from which the cloth of science. is woven.

The balance of references and citations in a single. year indicates one very important attribute of the network . Although most papers produced in the year contain a near- average number of bibliographic references, half of these are references to about half of all the papers that have been published in previous years. The other half of the references tie these new papers to a quite small group of earlier ones, and generate a rather tight pattern of multiple relationships. Thus each group of new papers is “knitted” to a small, select part of the existing scientific literature but connected rather weakly and randomly to a much greater part. Since only a small part of the earlier literature is knitted together by the new year’s crop of papers, we may look upon this small part as a sort of growing tip or epidermal Jayer, an active research front. I believe it is the existence of a research front, in this sense, that distinguishes the sciences from the rest of scholarship, and, because of it, I propose that one of the major, tasks of statistical analysis is to determine the mechanism that enables science to cumulate so ~much faster than nonscience that it produces a literature crisis.