252 



SCIENCE. 



[Vol. XII. No. 305 



uncertainty arises in that tine value 60.27 seems itself a little abnor- 

 mal. 



Referring to the equation found for this anemometer on this 

 machine, we have, 



V = o.gro + 1.02729c — 0.00076 c , 

 from which, when c = 60.4, 



— = 0.935- 



Using this co-efificient to reduce the contacts observed in the 

 second case to those corresponding to the velocity 62.24 of the first 

 case, we have 60.22 contacts as the number per hour. To be ac- 

 curate, the observed y!///7f/«rt' in the second case should also be 

 reduced to the velocity of the first case. Preserving its proportion- 

 ality to the arm-velocity, we find its value to be 4.67 kilometres per 

 hour. Hence it seems we should have 



Using the co-efficient 0.935 'o reduce contacts per hour to kilome- 

 tres per hour, we have corresponding to 0.18 contacts per hour a 

 velocity of 0.17 kilometres per hour. Hence finally, 



v., — z/j 0.17 



= = 0.71 = a. 



jTj; — ,r„ 0.24 

 The true Miiwi7id, according to this value, would be 5.2 per cent, 

 — a value practically the same as that found by Dohrandt; namely, 

 5 per cent. Considering that the latter value applies to much 

 larger anemometers than the former, the still outstanding difference 

 is probably due to the point already noted, that in the recent experi- 

 ments a Robinson anemometer, and not an air-meter, was used. 

 Further light would no doubt be thrown upon the question of the 

 value of the Mitiuind, if experiments were made in which the sta- 

 tionary air-meter is replaced by a small and very sensitive Robin- 

 son anemometer. 



It is hardly probable that the Mitwind is strictly tangential to 

 the path of the whirled anemometer : indeed, the writer has ob- 

 served a marked tendency to a spiral motion of the air and air-me- 

 ters with their axes tangent to the circular paths of the end of the 

 whirling arm, — get, as it were, only the tangential component. 



These considerations, it would seem, throw more or less doubt 

 upon the accuracy of the Mitwind corrections as obtained by both 

 experimenters, though in each case the results agree very well 

 among themselves. Unfortunately Mr. Dubinsky does not give 

 the numerical relations between the ' contacts ' and the revolutions 

 of the cups, by which it becomes possible to make comparisons 

 with anemometers of different construction in this respect. 



C. F. Marvin. 



Washington, D.C., Nov. 12. 



A Telescope for the New Astronomy. 



As we become accustomed to celestial phenomena, we find a 

 large number of faint appearances, upon the interpretation of which 

 our knowledge of the forces at work depends ; for instance, the 

 detection of the carbon atmosphere surrounding the sun, fore- 

 shadowed by Archimis in 1875 by the detection of the bright car- 

 bon band in the blue in the spectrum of the zodiacal light, inferred 

 by Lockyer in 1878 from a comparison of the solar and electric arc 

 spectra, indicated also by the observations of Schuster at Sohag 

 and by Abney in 1881, and finally worked out line by line by the 

 large instruments and photographic methods of Rowland ; or, 



again, the faint bright lines detected in the spectrum of many stars, 

 affording new ideas both as to the cause of the variability of the 

 stars' light and the classification of stellar spectra as worked out 

 from the study of meteorites by Lockyer. We find also that we 

 are not dealing with constant things : change and change again 

 are the only law. As the gravitational astronomer reaches his 

 conclusions by following the changing positions of the heavenly 

 bodies, so the physical astronomer must watch its ever-changing 

 appearance. Recall to mind the discussion over the well-known 

 comet spectrum, one astronomer averring from personal observa- 

 tion, deserving great respect, that the line belonged to the car- 

 bonic-oxide spectrum, while his rival assured us from equally 

 trustworthy sources that it was nothing if not hydrocarbon. 

 Science to-day tells us both were right, a slight change in the 

 density of the gas being sufficient to change the spectrum from 

 one to another. Our knowledge is therefore far from complete till 

 we have substituted the series for the single observation. 



But the human eye and the human brain are not sufficient — nay,, 

 are sometimes misleading — when complete and accurate detail 

 are desired. Our attention is attracted by the points raised by the 

 current theories of the day ; and much is left unnoticed, or, if 

 sought, is missed because one did not know where to look. The 

 history of (he discovery of the solar prominences, easily seen, after 

 discovery, by the same observer, using the same telescope with 

 which he had previously been unable to discover their existence, 

 presents an example. Photography to-day supplies a remedy. In 

 the hands of a master skilled both in the manipulation of the emul- 

 sion and the dye, its effect is not slight ; its advantage, much the 

 same as a balloon would give the voyager in the frozen seas, — 

 showing at a bird's-eye glance what years of travel could not show. 

 By it we may carry our best telescopes and our best seeing intO' 

 every home and school-room ; forming in his very youth the astron- 

 omer of the future, who shall work without telescope or observa- 

 tory ; rendering him familiar with those appearances which, not sO' 

 many years ago, enchained his ancestors. 



From its scientific side, of what great value has the chance de- 

 lineation of the tails of comets been in the hands of Bredechin .' 



It is not every telescope which is fitted to this end. It must be 

 pre-eminently a light-gatherer, which demands a large-sized object- 

 glass, with the attendant mounting, and yet possess the ease and 

 accuracy of motion of a sylph. It must be of great length, — thirty- 

 five or forty feet, — and yet from end to end have no mass of metal 

 which could produce an air-tremor. Yet such an instrument — the 

 El Dorado of full many an astronomer — to-day grows in the 

 workshop of an English astronomer. 



Seven feet in diameter, and of great thickness, is the reflecting 

 mirror ; forty feet, its length from end to end. Yet tube it has- 

 practically none. Tons in weight, it follows the steady pressure 

 of your little finger. Pedestal it^has none, but floats upon its polar 

 axis like a large warship ; this polar axis being little else than a 

 large boiler, so arranged, that. •' should it be thrown into the sea 

 in a given latitude, it would still point its axis to the pole." 



With an instrument of less than a fifth its power, Common's, 

 well-known photograph of the nebula in Orion was taken. With 

 one of less than a seventh of its capacity, the nebula in the Pleiades- 

 was discovered. The wonders reported from Mount Hamilton 

 show us what we may expect it to disclose. 



The instrument is secured to us through the esprit of a well- 

 known astronomer. Is it not possible that among the readers of 

 your journal may be found many who would contribute something 

 towards its endowment .' Of all our observatories, there is none 

 that is popular. Can we not make the largest glass the world has- 

 yet seen popular ? S. O. 



Bishops Potter, Stevens, and Robertson ; Presidents Mark Hopkins, Hitchcock, and Barnard; 

 Profs. Parker, Draper, and Beard; and thousands of the world's best brain workers, have used and 

 recommended CROSBY'S VITALIZED PHOSPHITES, for the relief of Nervous Derange- 

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