April 26, 1889.] 



SCIENCE 



^23 



must be determined by a dividing-engine. If a line can be dis- 

 tinctly seen, its wave-length can probably be thus determined with 

 as great accuracy as that of the position of the solar lines on the 

 map of Angstrom. In the spectrum of a Booizs 140 lines are 

 visible between the D and F lines. 



The classification of this large number of spectra is a matter of 

 no little difficulty. Slight differences exist in many stars, and cer- 

 tain stars appear to hold an intermediate position, so as to render 

 a rigorous division into classes impossible. On the other hand, 

 many stars appear to have identical spectra. The first step will 

 be to arrange the stars in groups, and then compare the best de- 

 fined spectra of different groups. A minute discussion and the 

 measurement of wave-lengths will be necessary only in the in- 

 vestigation of a comparatively small number of spectra. 



The 2S-inch reflecting telescope constructed by Dr. Draper was 

 assigned to the work on faint stellar spectra. During the first six 

 months of the year a careful study was made of this problem, and 

 the difficulties encountered bore evidence of the skill of Dr. Draper 

 in obtaining good results with this telescope. The best method of 

 using this instrument seemed to be a modification of the form first 

 tried by Dr. Draper, — a slit spectroscope from which the slit had 

 been removed. The rays from the mirror were rendered parallel 

 by a concave lens which replaced the objective of the collimator. 

 As this lens had the same focal distance as the objective of the 

 observing telescope, it was not necessary that either should be 

 achromatic. After long trials with this and other forms of appara- 

 tus, a spectrum was at length obtained showing good definition. 

 As the results were not better than those described above, and the 

 instrument, from its size, was slow in operation, the experiments 

 have not been carried further. 



The Bache telescope described above has proved an extremely 

 convenient instrument for various purposes. Besides the spectro- 

 scopic researches already mentioned, several other investigations 

 have been undertaken with it. Owing to its short focal length, it pos- 

 sesses many advantages over photographic telescopes of the usual 

 form. With exposures of an hour and a half, more stars were 

 photographed in the Pleiades than are given in the engraving accom- 

 panying the " Annual Report of the Paris Observatory of 1886," 

 although that work was based on photographs taken by MM. 

 Henry with exposures of three hours, and a telescope having an 

 aperture of 13 inches. Nearly twice as many stars were photo- 

 graphed in this region as were visible with the 15- inch telescope of 

 the Harvard College Observatory. The short focus of the tele- 

 scope also gives it especial advantages for photographing nebulse. 

 Twelve new nebulse were thus discovered in a region where but 

 eighteen were known before. Various other investigations, such 

 as a determination of the law of atmospheric absorption, have been 

 undertaken with the aid of this telescope. It has been so persist- 

 ently used in spectroscopic work that the other researches have 

 been neglected, especially those in which very long exposures were 

 required. Its removal to Peru now cuts it off for some time from 

 such use on the northern stars. Accordingly, Mrs. Draper has 

 procured a similar lens, which is now in the hands of the firm of 

 Alvan Clark & Sons for retouching and mounting. Several impor- 

 tant researches will be undertaken with this instrument. Photog- 

 raphy is now used in so many departments of astronomy, that a 

 general investigation of the photographic brightness of the stars 

 seems desirable. A plan has been proposed by which a single plate 

 will contain photographs of a number of regions one degree square, 

 but in different portions of the sky. Thus a series of standard 

 faint stars will be photographed, which can all be measured, and 

 reduced to the same scale. One or more photographs of the vicin- 

 ity of the north pole will be taken on each plate, and thus serve to 

 correct the results obtained on different plates. It is proposed in 

 this way to secure a series of standards of stellar magnitude at in- 

 tervals of about five degrees. A third lens of similar form, having 

 an aperture of four inches, will be attached to the telescope, with 

 which photographs on a smaller scale, but five degrees square, will 

 be taken simultaneously. These photographs will cover the entire 

 sky, and it is proposed to measure the photographic brightness of 

 all stars of the seventh magnitude, or brighter, which are repre- 

 sented on them. This investigation will have a special value in 

 connection with the photometric measures of the spectra described 



above. It is hoped also to photograph the entire northern sky by 

 means of the 8-inch telescope, with exposures of an hour. Each 

 plate covers a region nearly ten degrees square, of which the im- 

 ages in the central five degrees square are satisfactorily in focus. 

 One of the regions containing standard stars will appear in the 

 centre of each plate. By such a series of plates the photographic 

 brightness of any stars brighter than the fifteenth magnitude can 

 be determined on a uniform scale. The faintest stars photographed 

 will be nearly a magnitude fainter than the limit proposed by the 

 Astro-photographic Congress, so that all plates included in that 

 work can be reduced to a uniform system. The advantages of such 

 plates for studies of the distribution of the stars and other similar 

 investigations are obvious. 



From the above description it appears that the field of work of 

 the Henry Draper Memorial, as now extended, is almost boundless. 

 The problems to be investigated relate to the fundamental laws 

 regulating the formation of the stellar system. Questions of such 

 importance should be discussed on a sufficiently large scale, or the 

 results of the discussion will soon be superseded by a repetition of 

 the work. The liberal provision made for the Henry Draper Me- 

 morial permits the investigations to be planned on a scale which is 

 likely to avoid such an undesirable duplication of work. 



EXAMINATION AND EDUCATION.! 



For many years I have watched the examinations of young men 

 in our colleges, with reference to the award of prizes and honors, and 

 also with reference to the terms of admission to college and the 

 conditions of bestowing academic degrees. The conclusions to 

 which I have come are these : — 



Daily marks, jotted down by the instructor at the close of an 

 exercise, help him to form an accurate notion of the fidelity of his 

 scholars and of their intellectual growth ; but it is usually best for 

 him to keep these marks private, and simply for his own guidance, 

 lest by showing the record to his pupils he should accustom them 

 to the notion that work is over when they have learned the lesson, 

 solved the problems, or written the exercises acceptably. He must 

 not teach them to read for marks, — an odious habit. 



Examinations held at frequent intervals, say once a month, three 

 or four times a year, or at the end of a certain obvious block of work, 

 especially if preceded by a brief and spirited review, are as ser- 

 viceable to the scholar as to the teacher. The true condition of a 

 class can thus be ascertained and recorded. The scholar or his 

 advisers can be informed whether or not he excels, is passable, or 

 is deficient. The good students are thus encouraged to better 

 work : the poor students are warned before it is too late to recover 

 their standing. 



Yearly examinations accustom the scholar to hold on to the 

 knowledge that he has acquired. If rightly conducted, they remind 

 the pupil that he must carry in his mind the general principles and 

 the fundamental facts of the subject he has studied. A good ex- 

 aminer will put very different questions at an annual examination 

 from those he would set at the end of a month's study. He will 

 endeavor to ascertain whether the subject taught has been mastered 

 by the individuals examined, not whether every detail can be in- 

 stantly recalled. 



Special examinations at marked epochs in an education — such 

 as admission to college, competition for prizes, and the attainment 

 of a degree — encourage young men to put forth their highest and 

 best efforts, to make strong exertions, to overcome great difficul- 

 ties. As an important part of the business of life is the overcom- 

 ing of obstacles, so a good school or college should train its pupils 

 to meet and master tasks that are hard. The well-trained youth 

 will not shrink from such difficulties as he must encounter when he 

 becomes a physician, a lawyer, a statesman, a teacher, an engineer, 

 a philanthropist, an editor, a man of business ; in short, when he 

 takes an active part in the affairs of life. 



In selecting men for high stations, for appointments by the gov- 

 ernment, or for college fellowships, or for the position of teachers, 

 other tests than those of an examination must be employed. Evi- 

 dence that the candidate has exact knowledge, and that his knowl- 



I A contribution by President D. C. Oilman of Johns Hopkins University to he 

 American Supplement to the Nineteenth Century for March. 



