November 23, 191 1] 



NATURE 



113 



ploser examination, found to be in close agreement 

 iwith other evidence we have about the differences of 

 jlevel in the solar atmosphere. Lanthanum and 

 cyanogen are usually regarded as low-level con- 

 Ktituents, and they are also conspicuous in the present 

 instance in showingf consistently low velocities for 

 the solar rotation. This indicates that the period of 

 j-otation increases as we approach the surface, or that 

 the outer layers of the atmosphere rotate much more 

 rapidly than those lying close td' the photosphere. 

 iThese facts are in good accordance with the results 

 pbtained for hydrogen and the other substances which 

 are characteristic of high levels above the photosphere. 

 ;! All the observations may be well represented by a 

 plight modification of the Faye formula, showing that 

 it may be applied with great accuracy to determina- 

 ions of the sun's rotational velocity to within io° of 

 :ihe pole. The adopted formula for representing the 

 [Mount Wilson observatidns is — 



I = 1 1 -04° + 3 '50° cns^ (/), 



'here ^ is the daily angular velocity, and ^ the solar 

 latitude. In this connection it is of interest to review 



Fig. 2.— Curves represeniing the values of the angular velocity given by 

 the empirical formulie derived from the observations of Ha, A 4227, 

 and the reversing layer. For the last named the mean of the two 

 series of observations is used. 



le values of this equation which have been given by 

 jme of the more important determinations of the 

 lolar rotation made during the last century. 



Observer 



Cartington 



Spoerer 



Maunder 



Duntr 



Halm 



Adams (mean of two series). 



Adams A 4226 



Adams Ho 



{=14-42 -275 sin 7/4 

 {= 8"55 + 5"8o cos <p. 

 {= I2'43 4-2 01 cos- (p. 

 i=iO'6o + 4"2i cos'-^. 

 { + 1 2 "03 + 2 50 cos'^ (p. 

 i = 1 1 -04 + 3 '50 cos'-^ (p. 

 f = i2"5 + 2'4 cos- <p. 

 { = 1 3 6 + I '4 cos- <p. 



the main features outlined in this necessarily Diief 

 summary of a very extensive investigation. A word 

 of caution is given as to the interpretation of certain 

 results shown by the tables. Thus if the lines show- 

 ing systematic large or small values of the angular 

 velocity are specially considered, it is seen that there 

 is an apparent increase towards the sun's pole. Com- 

 parison of the results found for sun-spots, faculae, srd 

 the calcium flocculi gives the following sequence in 

 order of decreasing equatorial acceleration : (i) spots 

 and faculae, (2) A 4227, (3) calcium flocculi, (4) Ha. 

 The reversing layer shows a greater amount of equa- 

 torial acceleration than any of these. 



Charles P. Butler. 



MAGNETIC OBSERVATIONS AT THE COLABA 



OBSERVATORY.' 

 npHE two somewhat formidable volumes referred to 

 -^ below contain a most valuable compilation ol 

 observations extending over sixty years, together with 

 a discussion of the results presented in a form in 

 which they can be used in further investigations. 

 Observations on terrestrial magnetism were started 

 at the Colaba Observatory, Bombay, in 1840, but it 

 was not until the year 1846 that regular records were 

 obtained. When it was found that disturbances were 

 likely to be caused by the electric traction which was 

 being introduced in ISombay, it was decided to move 

 the observatory to a more suitable site at Alibdg, 

 about eighteen miles away; and after securing dupli- 

 cate records at the two stations in 1904 and 1905, the 

 magnetic work at Colaba was finally abandoned in 

 1906. The first volume, extending over 264 pages, 

 contains a complete description of the instruments and 

 processes of reduction. The methods employed are 

 described in great detail — some may think, perhaps, 

 with too great diffuseness — but many interesting 

 points are brought out incidentally. The complete 

 record, for instance, of the monthly values of the mag- 

 netic moment of one of the standard magnets, ex- 

 tending over nearly forty years, is probably unique. 

 This magnet does not show any tendency to approach 

 a steady state : it is rather the annual diminution 

 amounting to about the thousandth part of its value 

 which has become steady. 



Great attention is deservedly given to the tempera- 

 ture corrections. These were originally determined 

 by means of thermometers suspended on the wall of 

 the magnetometer room, and the corrections were 

 obtained by assuming that the magnets had the same 

 temperature as the walls. This — as is now found — 

 has led to errors. A remarkable discrepancy between 

 the diurnal variation deduced from eye observations 

 taken above ground, and that deduced from the photo- 

 graphic records taken in the magnetometer room, led 

 Mr. Chambers to suggest that the amplitude of the 

 variation might be different according as the magneto- 

 meter is placed above or below the surface of the 

 ground. Since the observatory was dismantled Mr. 

 Moos has made a careful comparison of the tempera- 

 ture variations observed by the thermometers on the 

 walls with those recorded by thermometers placed in 

 the exact position of the original magnets, and found 

 — as might have been expected — that the variations 

 here were smaller. Rectifying the previously applied 

 temperature corrections, it was found that the diurn.il 

 variations as observed in the two positions became 

 identical. 



1 " Magnetic Observations marie .it ihe Oovemmfnt ni)«ervatory, Bombay, 

 for the Period 1846 to 1905. and their T>i-^cuss!on." By N. A. F. Moos. Part i., 

 Magnetic Data and Instruments. Pp. v4-a6i + plaies. P.irt ii., The Phe 

 nomenon and its Discussion. Pp. xiv+vii+iv+265-7824-plates. (Bombay: 

 Government Central Prejs, 1910.) 



NO. 2TQ:C. VOT. 



