March 22, 1877] 



NATURE 



457 



centre ; this is why latterly I use exclusively cathetometric 

 telescopes, in which the distance of the eye-piece from the ob- 

 jeciive cannot undergo any change. On the other hand, it is pos- 

 sible to move the lunette if the cathetometer itself is in the rest 

 where it is fixed ; which is not seldom necessary in practice. By 

 using a considerable magnifier and an illutninator of the columns 

 of mercury very carefully combined, it is possible to observe the 

 columns with a precision carried to thousandths of a millimetre ; 

 so that the error in appreciating the height dees not exceed 

 001 mm. Everyone who has worked with the ordinary catheto- 

 meters and who has used their scales for measuring heights, knows 

 that the accuracy of the measurement by means of such apparatus 

 never exceeds ^V mm., and that often he makes errors which 

 reach tenths of a millimetre. It is sufficient to refer to the varia- 

 tions of temperature infallibly due to the presence of the observer. 

 In the construction applied by me, these reasons, as well as 

 many other causes of error, do not exist at all. 



Although for the barometers and the baromanometers I always 

 use tubes of large diameter, exceeding 17 and very often even 

 20 millimetres, nevertheless I have thought it proper to verify 

 the capillary depression of the mercury depending on various 

 diameters cf the tube and various heights of the meniscu«. A 

 very extensive research has been made in my laboratory by 

 Mile. Goutkovsky, and the results which she has obtained have 

 obliged me to change the data which we possess on the depression 

 of mercury. I cite one example from many which are in my 

 work on " The Barometric Levelling and on the Application of 

 the Syssotomer to that purpose." The diameter of the tube 

 being 8 606, and the height of the meniscus — 



o'6 08 i"o I '2 I "4 millimetre, 



the depressions are — 



o'i62 0-235 0'3i2 0380 0*458 ,, 

 numbers differing from those generally adopted, according to 

 which for a height of the meniscus i 'o, there ought to be a 

 depression of 0*460 for the diameter 8 606, 



De Mendeleeff 

 {7i? be continued.) 



OUR ASTRONOMICAL COLUMN 

 The Suspected Intra-Mercurial Planet. — M. Levarier 

 has issued an ephemeris of positions of the hypothetical plane^ 

 interior to Mercury, derived apparently from the two orbits to 

 which reference was made last week as representing the observa- 

 tions upon which the general formula was founded, with equal 

 precision, and if the planet should not be met with in transit 

 across the sun's disc between March 21 and 23, use may be 

 made of M. Leverrier's ephemeris to examine with large tele- 

 scopes the positions of the greatest elongation westward in the 

 two orbits. The differences of right ascension and declination 

 from the sun about these times are thus given : — 



The observation of Decuppis at Rome in 1839, one of the five 

 utilised by M . Leverrier, was communicated to the Paris Academy 

 of Sciences on December 16 in the same year. It is thus noticed 

 in the Comptes Rendus of that sitting : "M. Decuppis announced 

 that on October 2, while continuing the observations which he 

 has made upon the spots of the sun, saw a black spot, perfectly 

 round, and with well-defined contour, which advanced upon the 

 disc with rapid motion, so that it would have traversed the 

 diameter in about six hours. M. Decuppis thinks that the ap- 

 pearances which he has observed can only be explained by 

 admitting the existence of a new planet." The observation is 

 reproduced here, as it appears to have escaped the notice of 

 several writers who have recently entered upon this subject. 

 Ilaase mentions it, but does not give particulars. 



The observation by Mr. Joseph Sidebotham at Manchester, 



on March 12, 1S49, was communicated to the Literary and 

 Philosophical Society of that city, April i, 1873, and will be 

 found in the Prcceedings, vol. xii. p. 105. " A small circular 

 black spot " was " watched in its progress across the disc for 

 nearly half an hour," by Mr. Sidebotham and Mr. G. C. Lowe, 

 also a member of the same society. 



D'Arrest's Comet. — If this comet is not detected before moon- 

 light interferes in the mornings, it may probably be observed in the 

 middle of the ensuing month, where the sky is very transparent 

 down to the eastern horizon ; it will then rise rather more than 

 two hours before the sun, and the intensity of light will be greater 

 than when it was last seen by Prof. Schmidt at Athens in 

 December, 1870 ; still its distance from the earth will be con- 

 siderable (17). When theoretically brightest, in May, observa- 

 tions may be made at the observatories of the southern hemi- 

 sphere. At the Cape, Melbourne, and Sydney, the comet will 

 rise more than four hours before the sun ; the perihelion passage 

 takes place on May 10. The following positions willsufficiently 

 indicate its course about that time : — 



At Greenwich Noon. 



R.A. N.P.O. Distance from 



h. m. s. o , Earih. 



May 2 ... 23 18 16 ... 91 170 ... I "670 



6 ... 23 32 13 ... 90 3 1 "9 ... I '659 



10 ... 23 46 5 ... 89 47-8 ... 1-650 



14 ... 23 59 51 ... 89 48 .. 1-642 



18 ... o 13 28 ... 88 23-3 ... 1-635 



22 ... o 26 56 ... 87 43*6 ... 1-629 



26 ... o 40 14 ... 87 58 ... I -624 



The intensity'of light remains sensibly the' same during this 

 period. In August and September next observations may be 

 practicable with very powerful instruments, as the comet moves 

 from Taurus into Orion. 



According to the elements of M. Leveau, who has continued 

 the investigations on the motion of D'Arrest's comet, commenced 

 on its first discovery in the summer of 1851 by M. Villarceau, 

 the dimensions of the orbit in 1877 are as follow : — 



Semi-axis major ... ... ... ... 3-5414 



Semi-axis minor ... ... ... ... 2-7565 



Semi-parameter ... ... ... ... 2*1456 



i'erihelioii distance ... ... ... 1-3181 



Aphelion distance 57647 



The period of revolution in the ellipse of 1877 is 2434-2 days, or 

 6 664 years ; it has been lengthened 104 days since 1851, by the 

 effect of perturbation from the action of Jupiter, the principal 

 disturbance of its motion having taken place in the spring of 

 1 86 1, when the comet approached the planet within 0*36 of the 

 earth's mean distance froin the sun. 



Total Solar Eclipses. — It might be worth while to collect 

 together and discuss the various notices of the total solar eclipses 

 of 1386, January i, and 1415, June 7, in the same manner that 

 Prof. Schiaparelli and M. Celoria have done with the eclipses of 

 1239 and 1241. The eclipse of 1415 in particular was a very 

 notable one from the large excess of the moon's augmented 

 diameter over the diameter of the sun ; as Baron de Zach states, 

 "plusieurs historiens etpresque touslesastronomesenoutparle." 

 Both eclipses were total at Montpellier, not a common occurrence 

 at a particular place in an intei val of only twenty-nine years. 



METEOROLOGICAL NOTES 

 Mean Atmospheric Pressure in Russia in Europe. — 

 A paper on this subject, by M. Rikatcheff, appeared some time 

 ago in the Repertoriiim Jiir Meteorologie. The work is based on 

 monthly averages for various terms of years for thirty places in 

 Russia, to which are added the averages for thirty-three places 

 situated in other parts of Europe. A valuable part of the paper 

 is that which gives the details of the observations at each place, 



