June 27, 19 18] 



NATURE 



see how effective and close a union between our 

 countries of the Entente would in the end be wrought 

 ;ind consoHdaled by these organs of high industrial 

 control or co-ordination? 



In some of the principal industries, therefore, let this 

 first step be taken on the long rood still to be travelled. 

 To travel it to the end, once this first step is taken, wo 

 shall then be drawn by the shining goal itself that 

 has to be reached : that of the truly intimate union 

 of our two countries, and the federation of the peoples 

 of the Entente on which depend the liberty of the 

 peoples and the peaceful and just re-ordering of the 

 nations. Eugenio Rignano, 



Editor of the International Review ScietUia. 



The Eotvos Revolving Balance. 



In the i^sue of Nature for March 21 Prof. Boys 

 directed attention to a very interesting experiment per- 

 formed by Baron Eotvos, in which the oscillations of 

 a revolving balance were shown to be an effect of the 

 rotation of the earth. 



Precise details of the experiment are lacking, but 

 it would appear that the beam of the balance was 

 adjusted so that its centre of mass lay upon its hori- 

 zontal axis of swing, and that the latter was com- 

 pelled to revolve in its own horizontal plane with a 

 definite angular velocity. It was observed that oscil- 

 lations were set up the amplitude of which was limited 

 by the damping resistance of the air. 



In the article referred to Prof. Boys gave reasons 

 for thinking that the expression given by Eotvos for 

 the amplitude in terms of the physical constants in- 

 volved was incorrect, and offered another in its stead. 

 1 think, however, that there is little doubt that when 

 the experiment is performed in the way which the 

 published accounts indicate the Eotvos formula is 

 right. 



Suppose we take as a system of moving axes of 

 reference principal axes of inertia of the beam of 

 which one coincides with the axis about which the 

 beam swings. Let this be the axis of x, and let it 

 make at the time t an angle tot with a horizontal 

 line drawn to the west, w being the angular velocity 

 with which the balance revolves. Let the axis of s 

 make an angle yjr with the vertical ; then if Q is the 

 angular velocity of the earth and A the latitude of 

 the place of experiment, the angular velocities of the 

 axes are 



o)_,= -Q cos X sin 0)/ + \/^. 



0),,= -Q cos X cos mi cos V' + vii sin X + w) sin yj/. 



(Ji^= Q cos X cos fc)/ sin V^ + i'Q sin X + a>) cos ^. 



If A, B, C are the corresponding moments of inertia, 

 and if we represent the resistance of the air by a 

 couple - N^, we obtain" as the equation for small 

 oscillations of the beam about the horizontal 



AV^ + N\/r + (C - B)a)*\/r = (A + C - 8)0)12 cos X cos at. 

 Assuming the beam to be essentially a long, narrow- 

 rod, we may put B = o and C = A, and with these 

 simplifications we obtain for ^ the expression 



2A0 cos X sin W/N. 



It is seen at once that the expression is essentially 

 the same as that obtained by Eotvos. The terms repre- 

 senting the free oscillations are omitted, as such 

 oscillations will ultimately be damped out by the 

 resistance of the air. In simplifying the equation, the 

 assumption is made that AQ is small compared with 

 N It seems probable that Eotvos used a "small" 

 balance in order to ensure that this condition should 

 be satisfied, for if we compare similar l^alances 



NO. 2539, VOL. lOl] 



NecL* and AocI/>, where L denotes a linear dimension. 

 If this condition were not satisfied, the character of 

 the motion would be considerably modified. 



J. B. Dale. 

 King's College, June \1. 



I HAVE to thank Prof. Dale for pointing out the 

 very serious error that I made when I assumed that 

 the variation of centrifugal force was the only action 

 operative in the Eotvos revolving balance, and I must 

 apologise to Mr. Korda for having treated his account 

 of this beautiful device as inaccurate as well as in- 

 adequate. ^ C, V. Boys. 



The Discovery of the New Star m Aquila. 



Capt. E. V. Piper, of Fowey, Cornwall, was 

 obser\'ing meteors on the night of' June 7-8 between 

 i2h. 30m. and i3h. om. G.M.T., and saw seven. 

 He recorded a ist mag. one at i2lt. 45m., which shot 

 to just below Altair from a little above a bright star 

 to the west \yhich he could not identify. This star 

 had a green tinge, and was equal in lustre to Altair. 

 Though he knew the constellations and all the brighter 

 stars in this region very well, he was struck with the 

 strange object to the right of Altair. Mrs. Piper, 

 who came out on the balcony from which Capt. Piper 

 was observing, also remarked on the green colour and 

 flashing light of the star. 



Capt. Piper saw the star again on the evening of 

 June 8 at 9.18 p.m., and was puzzled at its appear- 

 ance, but considered that it meant some phenomenon 

 already well known to astronomers. On MondaA", 

 June 10, he saw an announcement in the newspapers 

 that a new star had been discovered in the position 

 where the strange object had attracted his notice on 

 the morning of June 8. 



The whole of the facts and circumstances of the 

 observation have been investigated by Mr. T. H. L. 

 Hony, of Fowev, who is an amateur astronomer, and 

 is convinced of the perfect trustworthiness of the 

 details. 



Capt. Piper has occasionally sent me accounts of 

 meteors, and they have been very good. It seems to 

 me that the difficult feature to understand in con- 

 nection with the obsor\-ation of the star on the morn- 

 ing of June 8 is that it was as bright as on the fol- 

 lowing night. We know that these objects rise verv 

 rapidly to a maximum. The Perseid nova of 

 February, iqor, increased from less than 12th magni- 

 tude on Februarv 20 to 27 magnitude on Februarv 21 

 after an interval of twentv-eight hours ! ' 



W. F. Denning. 



Bristol, Juno t8. 



The Food of the Rook. 



There is still so much difference of opinion among 

 those who, like the writer of the note in Nature of 

 June 6 (p. 271), have examined the contents of the 

 stomachs of rooks as to the economic position of 

 these birds that the time has come when a com- 

 mittee of scientific men should be invited to sift the 

 extensive evidence that is now available and issue a 

 report. 



I am in agreement with Dr. Long that the method 

 of balancing one grain of corn as beneficial against 

 one insect as injurious is most fallacious. The corn 

 found in the stomachs of rooks in the summer months 

 (Mav and June), and a great deal of the corn gathered 

 by the rooks on the roadside or after gleaning in the 

 autumn, would never be garnered by the farmer, but 

 an injurious insect that escapes the visitations of the 

 birds is always capable of considerable mischief. 



