32 2 



SCIENCE. 



[Vol. XIII. No. 325 



SCIENCE 



A WEEKLY NEWSPAPER OF ALL THE ARTS AND SCIENCES. 



PUBLISHED BY 



N. D. C. HODGES, 



47 Lafayette Place, New York. 



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Communications will be welcomed from any quarter. Rejected manuscripts will be 

 returned to the authors only when the requisite amount of postage accompanies the 

 manuscript. Whatever is intended for insertion must be authenticated by the name 

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 )ur correspondents. 



NEW YORK. April 26, 18 



No. 325. 



CONTENTS: 



■Composite Portraits of Washing- 

 ton 3T1 



(Congress of Electricians at the 



Pakis Exhibition 312 



An Electric Drawbridge 312 



A. New Form OF Secohmmeter 313 



The Rattlesnake's Rattle 315 



Washington's Signature 316 



Methods and Models in Geograph- 

 ic Teaching 317 



Health Matters. 



Bacteriology of Snow 318 



Scarlet-Fever 318 



Diphthena 318 



The Bacillus of Tuberculosis 319 



The Contagiousness of Tubercu- 



Lead-Poisoning 3 j 



Electrical News. 



Ayrton and Perry's Secohmmeter 

 ami Secohm Standard . . ... ,t 



Topeka Electric Railway 319 



Earthing Lightning-Conductors by 

 Means of Gas and Water Pipes. .. 319 



Notes and News 320 



The Henry Draper Memorial 322 



Examination and Education 323 



Ascent of the Kilima Ndjaro 324 



Stanley's Discoveries 325 



The Influence of Certain Drugs 

 ON Physical Strength and En- 

 durance 326 



Book-Reviews. 

 Francis Bacon, his Life and Philos- 

 ophy 327 



Curve Pictures of London for the 



Social Reformer 327 



Marriage and Divorce in the United 



States 



Among the Publishers . . 

 Letters to the Editor. 

 New Sources of Heat . . 



327 



THE HENRY DRAPER MEMORIAL. 



The third annual report, just published, shows that the re- 

 "-searches which constitute the Henry Draper Memorial have con- 

 •oisted for the last three years in the photographic study of the 

 -spectra of the stars. While this subject will continue to be the 

 principal one under investigation, Mrs. Draper has decided to ex- 

 •tend the field of work undertaken so as to include the study of the 

 other physical properties of the stars by photography. The first 

 research undertaken is now rapidly approaching completion, the 

 plans for the study of the southern stars have been matured, and 

 this study will soon be begun. The detailed study of the spectra 

 of the brighter stars is making progress, and a large piece of pho- 

 tometric work will soon be undertaken with a new telescope. 



The Bache telescope, which has an 8-inch photographic doublet 

 as an objective, is used for the catalogue of spectra of bright stars. 

 The photographs cover the entire sky north of —25'^, with exposures 

 of about five or ten minutes. About 28,000 spectra of 10,800 stars 

 have been examined, including nearly all stars visible in Cambridge, 

 of the seventh magnitude or brighter. The catalogue is now nearly 

 ready for the printer. 



In November, 1888, the photographs required to cover the sky 

 tiorth of the equator for the catalogue of spectra of faint stars were 

 nearly finished. It was expected that in two months the observa- 

 tions would be completed. The telescope, which was the same as 

 that used in the previous research, was, however, wanted for photo- 



graphing the solar eclipse of Jan. i, 1889. It was accordingly sent 

 to Willows, Gal., where it was mounted, and the greater portion of 

 the remaining photographs were taken there. It was then sent to 

 Peru. The few remaining photographs, including the repetition of 

 those found on further examination to be unsatisfactory, will be 

 taken in Peru. The sky from — 25° to the south pole will be 

 covered for bright stars as well, and the resulting photographs 

 sent to Cambridge and reduced, as in the case of the northern 

 stars. The advantages of discussing all stars from the north to 

 the south pole according to one system are very great, and are here 

 secured for the first time in so extensive an investigation. If no 

 unforeseen difficulty arises, the photographs will all be completed 

 during the next two years. 



The 1 1 -inch refractor, with one, two, or four large prisms over 

 its objective, has been employed in the detailed study of the spectra 

 of the brighter stars throughout nearly every clear night, until 

 stopped by the morning twilight : 685 photographs have been 

 taken, most of them with an exposure of two hours. With the 

 present photographic plates, about 570 stars north of — 30° are 

 bright enough to be photographed with one prism, 170 of them 

 with two prisms, and 87 of them with four prisms. To obtain the 

 best possible result, some of the photographs must be repeated 

 many times. The difficulty is increased by the invariably hazy ap- 

 pearance of the lines in some spectra, like that of a Agttilce, which 

 was at first attributed to poor definition of the photograph. It is 

 expected that the work will be completed during the next year by 

 original or repeated photographs of 228 stars with one prism, of 

 64 with two, and of 12 with four. In general, stars as bright as 

 the fourth magnitude can be satisfactorily photographed with one 

 prism, the spectra obtained being about an inch long. Fainter 

 stars, if of a bluish color, give sufficiently distinct images, in some 

 cases good results being obtained with stars of the seventh mag- 

 nitude. For example, fourteen stars in the Pleiades are well photo- 

 graphed with this apparatus. With four prisms, much longer 

 spectra are obtained, and many more lines are visible. But cer- 

 tain differences in the character of the spectra are better shown 

 with the smaller dispersion. Numerous photographs have been 

 taken of the variable stars Ceii and /3 Lyrce. The changes in 

 the spectrum of the latter star seem to be undoubted ; those of 

 Ceti, if any, to be slight. Various peculiarities in the spectra of 

 individual stars have been detected. One photograph of f Ursa 

 Majo7-ts shows the K line distinctly double, and others show it 

 single. Many photographs will be required to determine the law 

 of its variation, if this is due to changes in the star itself. Bright 

 lines were detected in the spectrum of Persei, putting it in a 

 class in which only two or three other stars are known to fall. In 

 the double star /3 Cygni the two components have spectra of differ- 

 ent types, — an important consideration in the theories regarding 

 their formation. The brighter component is of the second type ; 

 the fainter, of the first. 



Ordinary photographic plates are not sensitive to rays of much 

 greater wave-length than the F line, or 486. By staining the 

 plates with various coal-tar prbducts, the range of sensitiveness 

 may be greatly extended. With erythrosine, the spectrum extends 

 to the wave-length 590. The sodium line D is distinctly seen to 

 be double in the photographs of a Bootis and a Aurigce. Various 

 experiments were also made with cyanine, but the plates were not 

 sufficiently sensitive to give good results. The entire length of the 

 spectrum with four prisms, including the portion obtained by ery- 

 throsine, is about six inches and a half. 



A beginning has been made of the measures of the positions of 

 the lines in the spectrum. A scale of fortieths of an inch has been 

 ruled on glass, and the positions of the lines read off with the aid 

 of a magnifying-glass. Twelve of the photographs of a Cams 

 Majoris have been studied in this way. The spectrum of this 

 star is traversed by the hydrogen lines, which are strong, and by 

 other lines which are so faint that they are only visible when the 

 dispersion is large and the definition good. The catalogue thus 

 formed contains about 320 lines. The average deviation of the 

 measures of the same line on different plates is about 0.05 of a 

 millionth of a millimetre, or 0.05 centimetres on the scale of Ang- 

 strom's map. If the line occurs in the solar spectrum, these meas- 

 ures will generally identify it. In other cases the exact position 



