M 



AY 31, li 



■] 



SCIENCE. 



419 



objective and a 2-inch eye-piece. The measured part of the plate 

 is about a foot long, the plates being 19 inches long. 



All the spectrum photographs taken at different times coincide 

 perfectly, and this can be used for such problems as the determi- 

 nation of the atmospheric lines. For this purpose, negatives at 

 high and low sun are compared by scraping the emulsion off from 

 half the plates, and clamping them together with the edges of the 

 spectra in coincidence. The two spectra coincide exactly line for 

 line except where the atmospheric lines occur. 



This method is specially valuable for picking out impurities in 

 metallic spectra, using some standard impurity in all the sub- 

 stances to give a set of 'fiducial lines; or, better, obtaining the co- 

 incidence of all the metals with some one metal, such as iron. 

 Making the iron spectrum coincide on the two plates, the other 

 spectra can be compared. This is specially possible, because the 

 focus of a properly set up concave grating need not be altered in 

 years of use ; for, when necessary, it can be adjusted at the slit, 

 keeping the distance of the grating from the slit constant. 



The spectrum of the carbon poles is generally too complicated 

 for use with any thing except the more pronounced lines of metals, 

 there being, at a rough guess, io,ooo lines in its spectrum. How- 

 ever, in photographing metallic spectra, but few of these show on 

 the plate, as they are mostly faint. The spark- discharge gives very 

 nebulous lines for the metals. 



Most gratings are ruled bright in the higher orders ; but this is 

 more or less difficult, as most diamond-points give the first spec- 

 trum the brightest. Indeed, it is very easy to obtain ruling v.'hich 

 is immensely bright in the first spectrum. Such gratings might 

 be used for gaseous spectra. Short- focus gratings of five feet radius 

 of curvature, very bright in the first order, require only a fraction 

 of a second exposure for the solar spectrum, and the spectrum of 

 a gas can be obtained in less than an hour. H. A. Rowland. 



NOTES AND NEWS. 



A SCHOOL for boys will open Wednesday, July 3, 18S9, at North 

 Edgecomb, Me., and will continue through the long vacation. Its 

 primary object will be to fit boys for the college-admission exami- 

 nations in the fall ; but others who desire to advance in their 

 studies, or to make up deficiencies during the summer, will there 

 find an excellent opportunity. Especial attention will be paid to 

 those who have been conditioned in the spring examinations. The 

 staff of instructors will consist of four Harvard graduates, who are 

 specialists in their several departments, and experienced tutors. 

 The location affords good facilities for tennis and base-ball, as well 

 as for boating, bathing, and fishing. As an experienced man will 

 have special charge of the out-of-door sports of the students, a few 

 boys will be received who do not wish to study, but who desire to 

 pass the summer, or a portion of it, in a pleasant and healthful 

 locality which combines country and seashore advantages. For 

 further particulars, address Louis L. Hooper, Harvard University, 

 Cambridge, Mass. 



— It has been announced that in the event of the final loss of 

 the McGraw-Fiske suit, involving §1,500,000, bequeathed to the 

 library of Cornell, Mr. Henry W. Sage of Ithaca would pay for 

 the library building, to cost over §200.000, on which work has 

 begun. But it has not been made public till now, that, in addition 

 to standing the cost of the building, Mr. Sage offers, if the suit is 

 lost, to give the library an endowment of §300,000. If the McGraw- 

 Fiske suit is won, as is confidently expected, Mr. Sage's half a 

 million will probably come to the university for other purposes. 

 The giving of this sum will make Mr. Sage's benefactions to the 

 university amount to about $1,000,000 in cash, besides counsel and 

 services. 



— In the American Journal of Science for March, 1887, and the 

 London, Dublin, and Edinburgh Philosophical Magazitie for 

 the same month, iSIr. Henry A. Rowland has published a list of 

 standard wave-lengths, as far as could be observed with the eye, with 

 a few imperfectly observed by photography, the whole being re- 

 duced to Bell's and Pierce's values for absolute wave-lengths. Mr. 

 Bell has continued his measurements, and found a slightly greater 

 value for the absolute wave-length of the D line, and Mr. Rowland 

 has reduced his standards to the new values. Nearly the whole 



list has been gone over again, especially at the ends around the A 

 line and in the ultra-violet. The wave-lengths of the ultra-violet 

 were obtained by photographing the coincidence with the lower 

 wave-lengths, — a method which gives them nearly equal weight 

 with those of the visible spectrum. The full set of observations 

 will be published hereafter, but the present series of standards can 

 be relied on for relative wave-lengths to .03 division of Angstrom 

 in most cases, though it is possible some of them may be out more 

 than this amount, especially in the extreme red. As to the ab- 

 solute wave-length, no further change will be necessary, provided 

 spectroscopists can agree to use that of Rowland's table, as has 

 been done by many of them. By the method of coincidences with 

 the concave grating, the wave-lengths have been interwoven with 

 each other throughout the whole table, so that no single figure 

 could be changed without affecting many others in entirely differ- 

 • ent portions of the spectrum. The principal difference from the 

 preliminary table is in the reduction to the new absolute wave- 

 length, by which the wave-lengths are about i in 80,000 larger than 

 the preliminary table. It is hoped this difference will not be felt by 

 those who have used the old table, because measurements to less 

 than .1 division of Angstrom are rare, the position of the lines of 

 many metals being unknown to a whole division of Angstrom. As 

 the new map of the spectrum has been made according to this 

 new table, there seems to be no further reason for changing the 

 table in the future. No attempt has been made to reduce the 

 figures to a vacuum, as the index of refraction of air is imperfectly 

 known ; but this should be done where numerical relations of time 

 period are desired. In the column giving the weight, the primary 

 standards are marked S, and the other numbers give the number 

 of separate determination of the, wave-length, and thus, to some 

 extent, the weight. Many of these standards are double lines, and 

 some of them have faint components near them, which makes the 

 accuracy of setting smaller. This is specially the case when this 

 component is an atmospheric line whose intensity changes with the 

 altitude of the sun. The principal doubles are marked with d ; 

 but the examination has not been completed yet, especially at the 

 red end of the spectrum, and a table of the standard wave-lengths 

 is given on p. 78 of the May number of the " Johns Hopkins Univer- 

 sity Circulars." 



— Schneider & Co. of France have recently taken out a patent, 

 as we learn from The Enginecrittg and Mining Journal, for 

 manufacturing steel containing a variable portion of copper, which 

 is to be used in making artillery of large caliber, armor-plates, rifle- 

 barrels, and projectiles. Ordinary copper is used for the purpose, 

 care being taken to prevent it from oxidizing before it is mixed 

 with the steel in the crucible ; and the composition contains two to 

 four per cent of copper, the alloy being capable of far more resist- 

 ing power and more elastic and malleable than simple steel would 

 be. This new material will also probably be valuable for making 

 girders for building-purposes and ship-plates. 



— Mr. J. S. Ames, in writing of the concave grating in theory 

 and practice, says a word as to the difficulties of ruling gratings, 

 which may explain why so many orders received at the Johns Hop- 

 kins University for gratings remain unfilled. It takes months to 

 make a perfect screw for the ruling-engine, but a year may easily 

 be spent in search of a suitable diamond-point. The patience and 

 skill required can be imagined. For the past year, all attempts to 

 iind a point for the new ruling-engine have failed ; and it is only 

 within a few days that one has been found. Most points make 

 more .than one " furrow " at a time, thus giving a great deal of 

 diffused light. Moreover, few diamond-points rule with equal ease 

 and accuracy up hill and down. This defect of unequal ruling is 

 especially noticeable in small gratings, which should not be used 

 for accurate work. Again, a grating never gives symmetrical spec- 

 tra, and often one or two particular spectra take all the light. 

 This is of course desirable, if these bright spectra are the ones 

 which are to be used. Generally it is not so. These individual 

 peculiarities of gratings were fully treated by Professor Rowland 

 in his lectures during the spring term of 1S8S. and have been em- 

 bodied by him in a complete mathematical theory of the grating, 

 which he has nearly ready for publication. It is not easy to tell 

 when a good ruling-point is found ; for a " scratchy " grating is 



