148 



NATURE 



\June6, 1878 



Washington, and the presence in the country of a special 

 expedition composed of French astronomers. Judging 

 from the accounts published in the New York papers on 

 May 7, observations were more or less successful in many 

 astronomical institutions, both the first and last contacts 

 being generally well observed, and numerous photo- 

 graphs obtained during the passage of the planet across 

 the sun's disc. At Ogden, Utah, where the French 

 astronomers were located, the clouds prevented more 

 than imperfect observations of the first contacts ; but 

 those at egress were satisfactory. Up to one o'clock 

 only three photographs were obtained, but subsequently 

 as many as seventy-five were secured, and the results, as 

 a whole, were considered satisfactory. At the observatory 

 of Dr. Draper, Hastings, on the Hudson, a number of 

 observers, including Prof. Holden, of Washington, availed 

 themselves of the admirable instrumental resources, and 

 the weather being for the most part advantageous, very 

 good results attended their efforts : of eighteen negatives 

 taken by Dr. Draper several were particularly perfect. 

 In addition to observations at the U.S. Naval Observatory 

 Prof. Newcomb and assistants made satisfactory ones at 

 the office of the American Ephemeris in Washington, 

 noting the first internal contact at loh. 7m. 43s. a.m., 

 according to the New York Times, and the second 

 internal contact at 5h. 53m. 50s. P.M. 



The following differences between the calculated and 

 observed times of first internal contact have been ob- 

 tained by comparison with Leverrier's elements, with 

 Newcomb's value of the solar parallax; the Greenwich 

 mean time for the centre of the earth resulting from a 

 calculation of somewhat greater refinement than that 

 previously introduced in this column being 3h. i6m. I2*5s. 



Observed 



Place of G.M.T. Error of 



Observation. reduced to Calculatk n. 

 earth's centre, 

 h. m. s. s. 



Antwerp 3 15 46*0 + 26'5 Two observers. 



Christiania — 41*2 + 3i'3 " Apparent internal contact." 



,, — 52*9 . + 19*6 " True internal contact." 



Gottingen — 34'8 + 377 Prof. Klinkerfues. 



,, — 47*7 + 24*8 Boedclicker and Heidorn. 



Josephstadt — 48-5 + 24*0 Three obsei-vers. 



Kiel — 38'6 + 33^9 Planet round. 



„ — 53*3 + i9*2 " Deutlicher Lichtfaden." 



Palermo — 55-9 + i6"6 Spectroscope. 



,, — 46*1 +26*4 Ordinary telescopic method. 



SanFemando — 49-1 + 23*4 Geometrical contact. 



,, 3 16 1 1 "7 + o"8 Separation of limbs. 



_,,,.. „ ( Prof. Newcomb and assis- 



Washmgton 3 15 58-4 + 14-1 j ^^^^^ 



The Greenwich mean time of second internal contact 

 similarly calculated is loh. 43m. 57 'Ss., which, compared 

 with Prof. Newcomb's observations at Washington, shows 

 a difference of 4- I9'6s. Other observations of the second 

 internal contact given in the New York journals are either 

 provisionally reduced or apparently affected by typogra- 

 phical errors or errors of transmission. 



The Zodiacal Light and Sun-spot Frequency. — 

 In a letter addressed to Gruithuisen in February, 1839, 

 published by the latter in his Astronotnisches Jahrbuch 

 for 1840, Olbers remarks, "My grandson, Wilhelm 

 Focke, Doctor of Law, who with attachment and zeal often 

 contemplates and scrutinises the starry heavens, asserts 

 that the zodiacal light has been observed in January and 

 February with quite exceptional brightness;" which, 

 Gruithuisen observes in a note, is "a new confirmation of 

 Cassini's observation that the zodiacal light is much more 

 brilliant when numerous and large sun-spots are present, 

 and diminishes in brightness when the spots are few» 

 My observations show that during January and February 

 the sun has exhibited unusually large and numerous 

 spots," and he adds, "viel Licht und fast immer eine 

 grosse negative Refraction." This refers to Cassini's con- 

 cluding statement in his memoir entitled " D^couverte de 



la lumi^re celeste qui parait dans le Zodiaque." " It is a 

 remarkable circumstance that since the end of the year 

 1688, when this light began to grow fainter, spots have 

 no longer appeared in the sun, while in the preceding years 

 they were very frequent, which seems to support in some 

 manner the conjecture that this light may arise from the 

 same emanations as the spots and faail(z of the sun." 

 In a previous part of the memoir Cassini, endeavouring to 

 assign a possible cause for the appearance of the zodiacal 

 light, remarks that the observations of that century had 

 made known that the sun is not only the source of light, 

 but also of " une mati^re propre k terminer, k ddtourner, 

 et k rdflechir ses rayons;" and that "cette mati^re ne 

 coule pas toujours de la meme mani^re, mais qu'elle a 

 des vicissitudes sans r^gle, selon lesquelles nous voyons en 

 certain temps dans son disque des facules, qui sont plus 

 Claires que le reste de la surface, et des taches obscures 

 qui ne sont point pdndtr^es par sa lumi^re." And he 

 goes on to say that if the matter which is the subject 

 of this light is of the same nature as that which forms 

 ihe/aael(z and spots on the sun, it should be liable to the 

 same changes and irregularities. However inadequate or 

 incorrect is the explanation of the spots and faculae given 

 by Cassini, his conjecture that the brightness of the 

 zodiacal light varies with the number and magnitude of 

 the solar spots is worthy of note, though we do not re- 

 member to have seen any allusion to it in our popular 

 astronomical treatises. 



THE INTERNATIONAL GEOLOGICAL CON- 

 GRESS 

 THE time of the opening of this Congress in Paris has 

 been finally fixed by the local committee for the 

 29th August, and the Congress will remain in session 

 about two weeks. Further details as to organization and 

 place of meeting will soon be made public. Meanwhile, 

 it is announced that from the 20th August to the 15th 

 September, the library and reading-rooms of the Geolo- 

 gical Society of France, No. 7, rue des Grands-Augustins, 

 Paris, will be at the service of members of the Congress. 

 As before, it is requested that all those who desire to 

 take part therein will make it known to the general 

 secretary, Dr. Ed. Jannetaz, at the above address, where, 

 also, the subscription of twelve francs, required for each 

 member, may be sent to Dr. Bioche, treasurer. Ladies 

 are admitted to the Congress. 



The local committee add to the above announcements : 

 — There is reason to believe that the numerous collec- 

 tions of geology and palaeontology, minerals, rocks, 

 fossils,J maps, sections, plans, models in rehef, &c., 

 to be found in the Exposition Universelle, will realise 

 the expectations expressed in the circular of the Inter- 

 national Committee, of an International Geological 

 Exhibition. All exhibitors of such collections are re- 

 quested to send, as above, such lists as will enable the 

 secretary-general, Dr. Jannetaz, to prepare a special 

 catalogue of them for the use of the Congress. 

 T. Sterry Hunt, 

 Secretary of the International Committee 



A KINEMATICAL THEOREM 



TAKE a plane, and, for clearness of idea, consider it as 

 fixed horizontally. On this fixed plane lay another, 

 and throughout the subsequent movement let the surfaces 

 of the two planes always remain in contact. Now let 

 the upper plane, starting from any position, be moved 

 about in any manner whatever, making any number (A/') 

 of rotations, the points on it describing curves of any 

 desired degree of complexity on the lower plane ; and let 

 it finally settle down again into its initial position, the 

 curves described by* the points on it being, in conse- 

 quence, closed curves. Take the upper plane, and let us 

 investigate the position on it of those points which have 

 described curves of any given area {A) on the fixed plane. 



