ASTRONOMY. 403 



with no positive result. Mr. Backhouse says : " I consider the question 

 of the existence of Vulcan can only be settled by continued and system- 

 atic watching for its appearance in transit, as at the time of an eclipse 

 of the sun it may be too near that luminary to be visible." 



The Earth : Variability of terrestrial latitudes. — The question of the 

 variability of terrestrial latitudes was brought anew to the attention of 

 astronomers by the International Geodetic Conference at Rome in Oc- 

 tober, 1883. A plan for settling the question by observation was pro- 

 posed by M. Fergola, an Italian astronomer, which was, essentially, 

 that a careful series of observations should be made with ijrime vertical 

 instrument, by two co-operating observatories differing but little in 

 latitude though, perhaps, considerably in longitude. The same list of 

 stars was to be used at each j)air of such stations. . By repeating tbese* 

 observations after an interval of fifty years or more, tbe question of the 

 variability of latitudes would be subjected to a severe test. Theoret- 

 ically, periodical changes of latitude may occur, and an examination of 

 observations made at a number of Northern observatories during the 

 past seventy-five years — Konigsberg, Milan, Naples, Paris, Pulkowa, 

 and Washington — appears to confirm the existence of such changes. 

 At Pulkowa, which furnishes the most careful series of observations, a 

 diminution of the latitude of 0"-23, equivalent to about 23 feet, is indi- 

 cated between the years 1843 and 1872 ; but in all these cases the var- 

 iations are small, and we must be extremely cautious in ascribing them 

 to actual changes of latitude. A recent and very complete discussion 

 of the latitude of the Greenwich Observatory by Mr. Christie gives no 

 evidence of a secular change of latitude, and a later determination of 

 the latitude of the Washington Observatory (in 1883) also furnishes no 

 proof of a change. 



Prof. Asaph Hall, in a paper* read before the Philosophical Society 

 of Washington, February 28, 1884, has given a discussion of the obser- 

 vations tabulated by M. Fergola. His conclusion is that " observations 

 do not prove that latitudes are variable, and the evidence points rather 

 to other sources of small changes that may depend on the seasons. 

 Perhaps some of these may arise from the tables of refraction which 

 are in common use, and which are assumed to fit the whole earth." 



Some preliminary steps have been taken towards putting Pergola's 

 plan in operation at the observatories of Lisbon and Washington 

 (the difference of latitude being 11' 7"), but we believe no observations 

 have actually been made yet. 



Efect on the eartWs motion produced by small bodies passing near it. — 

 Professor Newton points outt that the space through which the earth 

 travels is traversed also by small bodies, or meteoroids. The impact of 

 these bodies upon the earth, and the consequent increase of the earth's 

 mass, have their effect upon tlie earth's motions, both of rotation aud 



*Amer. J. »S'ct., 3 s. vol. 29, p. 223-27 ; also Observatory 6, p. 113-17. 

 \4mer. J. >Soi., December, 1885, 3 b., vol. 30, p. 410-17. 



