Nov. 27, 1S84] 



NA TURE 



91 



Couchy, who, seventeen years ago, under the Empire, was 

 Director of the French Telegraphs. The charge for carrying a 

 letter to any place within the fortifications has been fixed at T,i. 

 The two extreme points in the service are about 11,000 metres 

 and the lime required for the delivery of a letter to the 

 remotes: place in the most unfavourable circumstances, and in- 

 cluding its conveyance from the nearest station, will be within 

 one hour. 



I m Si ientific Exhibition at Paris, always held on the occa- 

 sion of the grand soi ' Imiral Mouchez, Director of 

 the Paris ( observatory, will this year be under the management 

 of the French Electrical Society, and its exhibits will therefore 

 be confined to objects relating to that branch of science. 



PROF. Mell, Director of the Alabama Weather S 

 nounces, in Science, that through the liberality of the Chief 

 Signal Officer, an 1 of several railways, daily weather-signals, 

 predicting changes of weather and temperature, will be displayed 

 at over one hundred telegraph-stations in that State. The pre- 

 dictions will b the Director at an early hour every 

 morning from the Signal Office in Washington, and then promptly 

 distributed along the railways. By paying for the cost of the 

 signal-flags (about six dollars'), any town or telegraph-station 

 will receive free telegraphic warning of the daily weather changes. 

 Only about five minutes are required to set the flags. A similar 

 1 has been for some time in operation in Ohio and in pari 

 Ol 1 ennsylvania, and it will doubtless have further extension. 



mmander-in-Chief of the French army in Tonquin has 

 given orders to have a meteorological observatory erected in 

 Haiphong, the chief port in the delta of the Red River, to serve 

 as a ba-;s for a network of meteorological stations with which 

 it is intended to cover eventually the whole of Annam and Ton- 

 quin, and which will be in telegraphic communication with the 

 observatory in Hong Kong. 



In; series of illustrations of the methods and stages of in- 

 struction in handicraft an I technical training contributed by the 

 Austrian ( iovemment to the Health Exhibition is stated to have 

 been purchased by the Japanese Government from the Techno- 

 logical Museum at Vienna. The Japanese authorities have 

 also made numerous exchanges with the representatives of other 

 countries exhibiting at South Kensington. 



THE additions to the Zoological Society's Gardens during the 



past week include a Common Seal (Phoca vitulina) from British 



Sea-, presented by Mr. James Wyat ; two Barred I 'oves (Geopelia 



ilriata), three Pastern Turtle Doves [Turtur mtena) from lava, 



n id by Mi. I. mil Berg; a Green Monkey (Ctrcopithecui 



km i ) from West Africa, deposited; a Red-throated 



on (Chrysotu collaria) from Jamaica, a Red-tailed Amazon 



[CkrysJtis crythruia) from Brazil, three Blue Snow Geese (Chen 



cats) from Alaska, purchased ; a Bernier's Ibis {Ibis 



! from Madagascar, received in exchange. 



OCR ASTRO.XOMICAL COLUMN 



Tin Ei ii! 01 1 ih'cydides, B.C. 431, August 3. — There 



has been much discussion from time to time with reference to 



lar 1 clipse recorded by Thucydides in the first year of the 



' au war, and long identified as that which occurred 



I 3, B.C. 431. We are told, "the sun was eclipsed 



after midday, and having assumed a crescent for a, some of the 



in. having il 1 appeared, it again became full-orbed." This 



as not total, as has been frequently stated, but narrowly 



annular. Dr. 1 1 art wig in 1S59 calculated the circumstances 



according to the solar and lunar tables of Hansen, and his 



results were published, with those applying to other eclipses 



mentioned by Thucydides, in No. 1203 of Astronomist 'u JVacA- 



richten. The greatest phase, by his calculations, falls at 5I1. 9111. 



mean time at Athens, and the magnitude of the eclipse is 075, 

 rather small, it will be considered, for stars to have been brought 

 into view. But, when all the conditions of the case are borne 

 in mind, it would appear quite possible, to speak within bounds, 

 that Hansen's longitude of the moon may require at that epoch a 

 correction which would suffice, with the rapid descent of the central 

 line in latitude, to cause a great eclipse at Athens, leaving the 

 sun of crescent form, as Thucydides reports, but with the cres- 

 cent very narrow. In such a climate bright planets and stars 

 might well have been discerned. Venus was westward at an 

 altitude of some 35 , Mars would be near the western horizon, 

 Jupiter had set, while Saturn was near the meridian at an alti- 

 tude of something like 45". Of the stars, Spica, Arcturus, 

 Antares, and Vega were in favourable positions for observation. 



Sir George Airy informed the writer of these lines some years 

 since that, on the occasion of the partial eclipse of September 7, 

 1820, he "saw one or two stars" at Cambridge. On calculat- 

 ing the circumstances of the eclipse for that place, it appears 

 the magnitude was o'SS. This is an interesting case in point. 



Wolf's Comet. — A few week's since it was remarked in this 

 column that, according to the first elliptical orbit calculated by 

 Prof. Krueger, this comet would approach very near to the orbit 

 of Jupiter in about 209° heliocentric longitude, and great per- 

 turbation was possible early in the year 1S75, so that the comet 

 might not have been moving long in its present track. On this 

 subject Prof. Krueger, who has recalculated the elements of 

 the comet's orbit from a much wider extent of observation, 

 expresses himself as follows in No. 2629 of the Astronomischt 

 Nachrichten :— " In Nr. 782 der Nature (1S84, October 23) ist 

 hierauf bereits aufmerksaai gemacht worden ; ich hielt indessen 

 damals die ersten Elemente fur viel ungenauer, als sie wirklich 

 waren, und glaubte, dass Erbrterungen dieser Art noch etwas 

 aufzuschieben seien. Die nachfolgende Recruiting bestatigt in- 

 dessen die in der Nature ausgesprochene Vermuthung in iiber- 

 raschender Weise." In fact, Prof. Krueger finds by his new 

 orbit that on May 2S, 1875, the comet's distance from Jupiter 

 was less than 01 of the earth's mean distance from the sun, and 

 hence it is probable that before the spring of this year the comet 

 may have been describing a very different orbit to that in which 

 it now moves. This, as was before remarked, will form an 

 interesting subject of investigation, when definitive elements 

 have been deduced from a combination of all the observations of 

 the present appearance. 



In Prof. Krueger's last orbit, founded on observations to 

 November 7, the period of revolution is 2466x6 days, according 

 to which the comet would have been in perihelion about 

 February 16, 1878, in R.A. 23I1. 58m., Deck + 2', distant from 

 the earth 2-32, and under such circumstances not likely to have 

 been seen. We subjoin other elements of the orbit : — 

 Semi-axis major ... 35722 | Perihelion distance .. i'57'9 

 ,, minor ... 2-9596 Aphelion ,, .. 5-5725 

 Semi-parameter ... 2-4521 | Excentricity 0-559966 



Minima of Algol. — The following are approximate geo- 

 centric Greenwich times of minima of Algol, calculated from 

 elements upon which the later observations of Schmidt have 

 been brought to bear : — 



Dec. 23 



Jan. 



Jan. 26 



29 



Feb. 1 



h. m. 



i« 35 

 15 2 4 

 12 14 



9 3 



5 52 



THE WAVE THEORY OF LIGHT 1 

 ""THE subject upon which I am to speak to you this evening s 

 A happilyfor me not new in Philadelphia. The beautiful lectures 

 on light which were given several years ago by President Morton, 

 of the Stevens' Institute, and the succession of lectures on the 

 same subject so admirably illustrated by Prof. Tyndall, which 

 many now present have heard, have fully prepared you for any- 

 thing 1 can tell you this evening in respect to the wave theory of 

 light. 



It is indeed my humble part to bring before you some mathe- 

 matical and dynamical details of this great theory. 1 cannot 

 have the pleasure of illustrating them to you by anything compar- 



1 A Lecture delivered at the Academy of Music, Philadelphia, under the 

 auspices of the Franklin Institute, September 29, 1884, by Sir William 

 Thomson, F.R.S., LL.D. 



