34 



NA TURE 



[May 12, 1S87 



the references to these plates, and the photographic 

 brightness of the star. 



(2) Catalogue of Spectra of Faint Stars. — This work 

 resembles the preceding, but is much more extensive. 

 The same instrument is used, but each region has an 

 exposure of an hour, the rate of the clock being such that 

 the width of the spectrum will be as before o"i cm. Many 

 stars of the ninth magnitude will thus be included, and 

 nearly all brighter than the eighth. In one case, over 

 three hundred spectra are shown on a single plate. 

 This work has been carried on only in the intervals when 

 the telescope was not needed for other purposes. 99 

 plates have however been obtained, and on these 4442 

 spectra have been measured. It is proposed to complete 

 the equatorial zones first, gradually extending the work 

 northward. In all, 15,729 spectra of bright and faint 

 stars have been measured. 



(3) Detailed Study of the Spectra of the Brighter Stars. — 

 This work has been carried on with the ii-inch photo- 

 graphic telescope used by Dr. Draper in his later re- 

 searches. A wooden observatory was constructed about 

 20 feet square. This was surmounted by a dome having 

 a clear diameter of 18 feet on the inside. The dome had 

 a wooden frame, sheathed and covered with canvas. It 

 rested on eight cast-iron wheels, and was easily moved 

 by hand, the power being directly applied. Work was 

 begun upon it in June, and the first observations were 

 made with the telescope in October. Two prisms were 

 formed by splitting a thick plate of glass diagonally. 

 These gave such good results that two others were made 

 in the same way, and the entire battery of four prisms is 

 ordinarily used. The safety and convenience of handling 

 the prisms is greatly increased by placing them in square 

 brass boxes, each of which slides into place like a drawer. 

 Any combination of the prisms may thus be employed. 

 As is usual in such an investigation, a great variety of 

 difficulties have been encountered, and the most im- 

 portant of them have now been overcome. 



(4) Faint Stellar Spectra. — The 28-inch reflector will 

 be used for the study of the spectra of the faint stars, and 

 also for the fainter portions near the ends of the spectra 

 of the brighter stars. The form of spectroscope men- 

 tioned above, in which the collimator and slit are replaced 

 by a concave lens, will be tried. The objects to be 

 examined are, first, the stars known to be variable, with 

 the expectation that some evidence may be afforded of 

 the cause of the variation. The stars whose spectrum is 

 known to be banded, to contain bright lines, or to be 

 peculiar in other respects, will also be examined system- 

 atically. Experiments will also be tried with ortho- 

 chromatic plates and the use of a coloured absorbing 

 medium, in order to photograph the red portions of the 

 spectra of the bright stars. Quartz will also be tried to 

 extend the images towards the ultra-violet. 



(S ) Absorption Spectra. — The ordinary form of com- 

 parison spectrum cannot be employed on account of the 

 absence of a slit. The most promising method of deter- 

 mining the wave-lengths of the stellar spectra is to inter- 

 pose some absorbent medium. Experiments are in pro- 

 gress with hyponitric fumes and other substances. A 

 tank containing one of these materials is interposed, and 

 the spectra photographed through it. The stellar spectra 

 will then be traversed by lines resulting from the absorp- 

 tion of the media thus interposed, and, after their wave- 

 lengths are once determined, they serve as a precise 

 standard to which the stellar lines may be referred. 

 The absorption-lines of the terrestrial atmosphere would 

 form the best standard for this purpose if those which are 

 sufficiently fine can be \ holographed. 



(6) Wave-Lengths. — The determination of the wave- 

 lengths of the lines in the stellar spectra will form an 

 important part of the work which has not yet been begun. 

 The approximate wave-lengths can readily be found from 

 a comparison with the solar spectrum, a sufficient number 



of solar lines being present in most stellar spectra. As a 

 difference of one ten-millionth of a millimetre in wave- 

 length exceeds half a millimetre in Figs. 5 and 6 of the 

 accompanying plate, the readings may be made with 

 considerable accuracy by a simple inspection. For 

 greater precision special precautions are necessary on 

 account of the deviation caused by the approach and 

 recession of the stars. The deviation found by Dr. 

 Huggins in the case of Sirius would correspond to a 

 change in the position of the lines of Figs. 5 and 6 of 

 about half a millimetre. If, then, satisfactory results are 

 obtained in the preceding investigation, the motion of 

 the stars can probably be determined with a high degree 

 of precision. The identification of the lines with those 

 of terrestrial substances will of course form a part of the 

 work, but the details will be considered subsequently. 



From the above statement it will be seen that photo- 

 graphic apparatus has been furnished on a scale un- 

 equalled elsewhere. But what is more important, Mrs. 

 Draper has not only provided the means for keeping 

 these instruments actively employed, several of them 

 during the whole of every clear night, but also of reducing 

 the results by a considerable force of computers, and ol 

 publishing them in a suitable form. A field of work o\ 

 great extent and promise is open, and there seems to be 

 an opportunity to erect to the name of Dr. Henry Draper 

 a memorial such as heretofore no astronomer has received. 

 One cannot but hope that such an example may be imi- 

 tated in other departments of astronomy, and that here- 

 after other names may be commemorated, not by a need- 

 less duplication of unsupported observatories, but by the 

 more lasting monuments of useful work accomplished. 

 Edward C. Pickering, 

 Director of Harvard College Observatory. 



Cambridge, Mass., U.S.A., March i, 1887. 



SCIENCE AND GUNNER V. 

 I, 

 T N the last lecture which Prof. Tyndall delivered at the 

 ■^ Royal Instituti on, he expressed a doubt as to whether 

 extensive reading and study had not a tendency to hamper 

 original genius, whether doctrines handed down for 

 generations as articles of faith, which it would be heresy 

 to dispute, had not materially checked the progress of 

 science. Had he wished to illustrate his theory, he could 

 not have had better examples than are to be found in the 

 administration of our naval and military systems. It has 

 been a reproach to us, as by far the greatest maritime 

 nation of the world, that we have no School of Ship- 

 building, that, until quite recently, naval officers have had 

 no instruction except such as they could get in the practical 

 execution of their duties, and no method existed of testing 

 their knowledge except such rough-and-ready examina- 

 tions as their superior officers could administer. Yet 

 under these seeming disadvantages the Navy and the 

 merchant service have kept in the forefront of progress, 

 and have adopted all the newest discoveries of science, 

 or of practical skill, as fast as they have been brought to 

 light. 



On the other hand, the officers of Artillery and Engineers 

 have long been considered as belonging to the scientific 

 branches of the service ; they have been regularly trained 

 in schools in which theory and history have been taught, 

 and the consequence seems to be that it is most difficult 

 to make the departments with which they are connected 

 move with the times. How else can it be explained that 

 we have adhered to wrought iron as a material for guns, 

 and to muzzle-loaders, long after nations esteemed semi- 

 barbarous have used steel and constructed breech- 

 loaders? or how can we explain the waste of millions in 

 constructing fortifications of patterns long obsolete, and 

 which show no more originality than that exhibited in using 



