May 29, 1879] 



NATURE 



99 



appearance, in this instance the rear being brought up by 

 the halt and lame : crippled birds that have lost a greater 

 or less number of their wing or tail feathers, some toes, 

 or even a whole foot. 



All this is very strikingly exemplified here by the black- 

 bird, for instance, with its varying dress according to age 

 and sex, and this might with some attention be observed 

 at other places also, though in the middle and south of 

 England and Germany such observations become greatly 

 more complicated, on account of the immigrants from 

 the north mixing with such of the same species as have 

 been breeding in these more southern latitudes, and where 

 the grand opening migratory rush, as witnessed here in 

 full original purity, has more or less relaxed in a con 

 amore travelling by easy stages. H. Gatke 



Heligoland, May 7 



THE U.S. NATIONAL ACADEMY 



ONE of the chief scientific events of the year in the 

 United States is the annual meeting of the National 

 Academy of Sciences, the most select scientific body in 

 America, election to which is regarded as stamping 

 a man as an acknowledged leader in science. This 

 year the meeting took place at Washington from 

 April 15 to 18, the acting president being Prof. O. C. 

 Marsh, who opened the proceedings with a review of the 

 Academy's official work during the previous year. He 

 had to record the great loss sustained by the Academy in 

 the death of its president, Prof. Joseph Henry, on May 

 13 last year. Henry had been president of the Academy 

 for ten years. One of the principal functions of the 

 Academy during the past year was the consideration of a 

 plan for the reorganisation of the U.S. Surveys, to which 

 we have already referred at length. 



At the meeting of the Academy in April last year a 

 resolution was adopted authorising the appointment of a 

 committee to consider a plan proposed by Prof. Newcomb 

 for determining the distance of the sun by measuring the 

 velocity of light. In accordance with this vote. Prof. 

 Marsh appointed as members of the committee, President 

 F. A. P. Barnard, Professors Wolcott Gibbs, Henry 

 Morton, George F. Barker, and E. C. Pickering. Their 

 report was so favourable to the plan proposed that Prof. 

 Marsh sent it to the Secretary of the Navy for transmis- 

 sion to Congress. An appropriation of 5,000 dels, for the 

 required purpose was thus secured, and the work of con- 

 structing the necessary apparatus will be commenced as 

 soon as the appropriation is available. The expenditure 

 of the funds is entrusted to the Secretary of the Navy. 

 It is hoped by those who proposed this plan that the ex- 

 periments will lead to a more accurate determination of 

 the distance of the sun than can be obtained by any other 

 method known to astronomy. 



Prof. William B. Rogers was elected President of the 

 Academy, to fill the vacancy caused by the death of Prof. 

 Henry. The election is a deserved tribute to Prof. Rogers, 

 who has for half a century held a prominent place among 

 American men of science. He was for many years a 

 leader among American geologists in adopting the modern 

 theories of evolution, and defended his views with rare 

 eloquence as well as strong argument. During his con- 

 nection with the Massachusetts Institute of Technology 

 (1862-68), the health of Prof. Rogers became s» much 

 impaired that he was obliged to withdraw from all studious 

 pursuits for a long period. His recovery of health was 

 the occasion of hearty congratulation in 1875, when he 

 was for a second time elected President of the American 

 Association for the Advancement of Science. The new 

 president is loved by everybody, is venerable with silver 

 locks, and still retains the silver-tongued eloquence for 

 which he used to be famous. But he is by no means 

 rugged, and has to take care not to over-exert himself. 



Many valuable papers were read during the meeting of 



the Academy, but our space will only permit of our refer- 

 ring to a few. We append a complete list, and those who 

 desire a complete report of the Academy's proceedings 

 will find it in Science News of May i and following 

 numbers. 



Two papers were presented by Mr. Peirce, entitled respec- 

 tively, " On Ghosts in Diffraction Spectra" and "Comparison 

 of VVaveLengths with the Metre." It is well known to users 

 of diffiaction spectroscopes that ghosts of the lines appear in 

 the images. Mr. Peirce has investigated this subject from a 

 mathematical point of view, and he presented to the Academy a 

 series of calculations based on the conditions which call forth 

 these ghosts, and concluding with formulje for determining their 

 positions. In conjunction with Mr. Rutherfurd, Mr. Peirce has 

 been investigating the relation of the wave-lengths of light to 

 the metre. The object is to obtain a basis for measuring the 

 standard metre. The metres that have been issued as standards 

 change in length after a lapse of time. The German metre is said to 

 differ from the French metre by one 25,000th. Mr. Peirce pro- 

 ceeded on the assumption that the wave-lengths of light are of 

 a constant value. Certain questions have arisen in the course of 

 this research. It was necessary to ascertain whether the spectral 

 lines were fine enough to serve the purpose. There was a doubt 

 as to whether the lines were displaced by "ghosts," and this led 

 to the mathematical inquiry, previously alluded to, which has 

 defined the position of ghosts relatively to the lines. Again, it 

 was found needful that the spectrum to be observed should be at 

 its maximum of brilliance. It had been noticed that two spectra 

 composing a pair (that is, of the same order) are usually of dif- 

 ferent brightness, the right side spectrum differing from the left 

 side one. This was specially true of spectra obtained from ruled 

 glass ; those from speculum metal were not so notably diverse 

 in brightness. Examination showed that this characteristic was 

 due to a difference in the sides of the groove ruled in glass. The 

 diamond, in ploughmg through the surface, raises a burr on the 

 side of the furrow, and hence makes the two sides of the cut of 

 unequal height. At first it was attempted to remove this imper- 

 fection by rubbing off' the burr ; but it was found that the mate- 

 rial of the burr went to fill up the groove, and thus rendered the 

 glass plate unserviceable. But, by first filling the groove with 

 black-lead, then polishing off' the burr, and finally removing the 

 black-lead, plates were obtained that gave spectra of the utmost 

 brilliancy, and the right and left spectra of each pair did not 

 diff"er in brightness firom each other. Mr. Peirce also gave the 

 particulars of other improvements recently made in spectro- 

 scopic apparatus. One of these involved the construction of 

 glass circles, and the work was so delicate that a well-known 

 instrument maker had failed in four attempts. A method was 

 described by which the accurate focussing of the heliostat — a 

 matter of great importance — had been satisfactorily attained. 

 The experimenters have succeeded in measuring a number of 

 decimetre scales by centimetres. The probability of a single 

 error is within the fiftieth part of a micron. (A micron is as 

 much smaller than a millimetre as the latter is less than a metre.) 

 Means have been devised which keep the apartment, where the 

 experiments are made, at a fixed temperature, within one-tenth 

 of a degree of Fahrenheit. With a sufficient number of obser- 

 vations, and the use of apparatus having their latest improve- 

 ments, these experimenters hope to attain the object of their 

 research, and limit the error to one-millionth part of a wave- 

 length. 



Prof. E. C. Pickering's paper on eclipses of Jupiter's satel- 

 lites was one of considerable importance. He showed the value 

 of the photometric method of observing these eclipses, and the 

 valuable data that might be obtained by improvements in this 

 method, both as to the sun's distance and as to Jupiter himself 

 and his satellites. 



In a paper on the winds on Mount Washington compared 

 with the winds near the level of the sea. Prof. Elias Loomis 

 came to the following conclusions : — I. In a majority of the 

 cases where an area of low barometer passes over New England, 

 attended by the usual circulating winds at the surface stations, 

 this system of circulating winds does not extend to a height of 

 6,000 feet. 2. This system of circulating winds extends to the 

 greatest height when the depression of the barometer is unusually 

 great. 3. When, during the progress of an area of low pres- 

 sure, a system of circulating winds reaches to the summit of 

 Mount Washington, the change of wind to ths east quarter 

 usually begins at the surface stations eleven hours sooner than 

 on the summit of the mountain ; and the change back from east 



