398 



SCIENCE. 



[Vol. XIV. No. 358 



The United States electric-light projector is shown in Fig. 2. It 

 has both a horizontal and vertical motion, so that the light can be 

 thrown in any direction. It carries a focusing-lamp in a parabolic 

 reflector. When out of service, the case is rigidly locked in posi- 

 tion by clamps at the side and a catch at the base, protecting it 

 against the jarring of a sea-way or otherwise. The glass face is 

 in strips to avoid cracking from unequal expansion. Its hinges 



FIG. 2. — ELECTRIC PROJECTOR. 



are made to act both as hinges and latch, so that by drawing 

 a pin the face can be opened on either side at will. All adjust- 

 ments are outside the case, so that the doors leading to the lamp- 

 works need not be opened. The lamp requires forty volts, and the 

 resistance-box shown in the cut adapts it to any circuit. 



TWENTY YEARS.i 



A REMINDER that to-day is the twentieth anniversary of the first 

 issue of Nature will not, perhaps, be without interest to our readers, 

 and certainly affords food for reflection to those who in various 

 capacities have been more or less closely connected with this jour- 

 nal from the first. 



"When another half-century has passed," said Professor Hu.x- 

 ley in our first number, "curious readers of the back numbers 

 of Nature will probably look on our best ' not without a smile.' " 



It will probably be so ; but, though twenty years is hardly a 

 sufficient interval to make our smiles at our earlier efforts super- 

 cilious, it is enough to test whether progress has been made, and 

 whether the forward path is pursued with growing or with waning 

 force. 



As regards this journal itself, we may claim that it has not dis- 

 appointed the hopes of its founders, nor failed in the task it under- 

 took ; and we make this claim all the more emphatically because 

 we feel that what has been accomplished has not been due to our 

 own efforts so much as to the unfailing help we have always re- 

 ceived from the leaders in all branches of natural science. This 

 help has not been limited to their contributions to our columns, but 



1 From Nature, Nov. 7, 1SS9. 



has consisted also of advice and suggestions which have been freely 

 asked and as freely given. Not the least part of our duty, and 

 even privilege, to-day, is to state openly how small our own part 

 has been, and to render grateful thanks to those to whom it is 

 chiefly due that Nature has a recognized place in the machinery 

 of science, and has secured an audience in all parts of the civihzed 

 world. 



We do not wish, however, to narrow our retrospect of the last 

 twenty years by confining our attention to the measure of success 

 which these pages have won. It has been attained, as we have 

 shown, by the aid of nearly all the best-known scientific writers 

 and workers, not in Britam only, but in many countries old and 

 new ; and we cannot believe that they would thus have banded 

 themselves together, if evidence had not been given of an honest 

 desire for the good of science and for the " promotion of natural 

 knowledge," or if the attainment of these objects had not been re- 

 garded by us as of more importance than a journalistic success. 

 Thus, on its twentieth birthday, we would think not so much 

 of the growth of Nature as of the advance which in the last twenty 

 years it has chronicled. 



A formal history of science for that period would be a formid- 

 able task, but it is already possible to discern what will probably 

 appear to posterity to be the most salient characteristics of the last 

 two decades. 



In the physical sciences, the enormous development of the atomic 

 theory, and the establishment of a connection between the theories 

 of electricity and light, are perhaps the two main achievements of 

 the years we are considering. Methods of accomplishing the at 

 first sight impossible task of measuring atomic magnitudes have 

 been devised. Our own volumes contain some of the most inter- 

 esting papers of Sir William Thomson on this subject ; and the 

 close agreement in the results attained by very different methods is 

 sufficient proof, that, if only approximations, they are approxima- 

 tions we may trust. The brilliant vortex atom theory of Sir Wil- 

 liam Thomson has not as yet achieved the position of a proved 

 hypothesis, but has stimulated mathematical inquiry. A number 

 of very powerful researches have added to our knowledge of a 

 most difficult branch of mathematics, which may yet furnish the 

 basis of a theory which shall deduce the nature of matter and the 

 phenomena of radiation from a single group of assumptions. 



The theory of gases has been extended in both directions. The 

 able attempt of Van der Waals to bring both vapor and liquid 

 within the grasp of a single theory is complementary to the exten- 

 sion by Crookes, Hittorf, and Osborne Reynolds, of our knowledge 

 of phenomena which are best studied in gases of great tenuity. 



The gradual expansion of thermodynamics, and in general of the 

 domain of dynamics from molar to molecular phenomena, has been 

 carried on by Willard Gibbs, J. J. Thomson, and others, until, in 

 many cases, theory seems to have outrun not only our present ex- 

 perimental powers, but almost any conceivable extension which 

 they may hereafter undergo. 



The pregnant suggestion of Maxwell that light is an electro- 

 magnetic phenomenon has borne good fruit. Gradually the theory 

 is taking form and shape ; and the epoch-making experiments of 

 Hertz, together with the recent work of Lodge, J. J. Thomson, and 

 Glazebrook, furnish a complete proof of its fundamental hypotheses. 

 The great development of the technical applications of electricity 

 has stimulated the public interest in this science, and has necessi- 

 tated a more detailed study of magnetism and of the laws of peri- 

 odic currents. The telephone and the microphone have eclipsed the 

 wonders of the telegraph, and furnish new means of wresting fresh 

 secrets from nature. 



Science has become more than ever cosmopolitan, owing chiefly 

 to the imperative necessity for an early agreement as to the values 

 of various units for a common nomenclature, and for simultaneous 

 observations in widely separated localities. International confer- 

 ences are the order of the day, and the new units which they have 

 defined are based upon experiments by many first-rate observers in 

 many lands, among whom the name of Lord Rayleigh stands second 

 to none. 



On the side of chemistry, the periodic law of Mendeleeff has be- 

 come established as a generalization of the first importance, and the 

 extraordinary feat of foretelling the physical properties of an as yet 



