August 28, 1.9 13] 



NATURE 



661 



proportional to v'H for the former branch, and to H 2 

 for the latter, showing that the singular case dis- 

 covered by Gmelin is not confined to the satellites of 

 the yellow line 5790. The same remark applies to the 

 satellite —242 of the green line; the (— ) branch be- 

 comes fainter with increase of the field, and is para- 

 bolic in the sense above mentioned, the ( + ) branch 

 increases in brightness with the field, and the wave- 

 length goes on increasing until it reaches a maximum, 

 whence it gradually returns to the initial value in 

 H = 24,000, and decreases farther at a constant rate. 

 The (4-) branch becomes ultimately parallel to the 

 principal line P_,. The direction taken by this 

 Branch ultimately coincides with that of the ( — ) 

 branch of the satellite, —74; on approaching the ( + ) 

 branch of —242, this ( — ) branch of —74 becomes 

 fainter, and is finally lost to view; the other branch 

 of —74 runs probably parallel to P + l , and increases in 

 intensity. 



The satellites —26 and 4-78 have both a curved 

 branch towards the negative side, and a straight 

 branch on the positive side, both being parallel to P„. 

 Thus in these lines the different branches to which 

 the satellites are divided ultimately run parallel to the 

 principal lines, whether the vibration takes place 

 parallel or perpendicular to the direction of 

 the magnetic force. This stage is reached earlier 

 in the latter than in the former, as an inspection of 

 the figures will show. The same holds good also 

 for the strong satellites of the mercury line 4359. 

 On reaching this stage, the change in wave-length 

 takes place proportional to the corresponding change 

 in magnetic field, and the separation becomes ulti- 

 mately normal. 



It is in the transition from zero field to this final 

 stage that the separation of the satellite takes place 

 in a singularly anomalous manner, that we seldom 

 meet with in the separation of the principal lines. 



This fact will have an important bearing on the 

 elucidation of the nature of the satellite, and probably 

 may have an intimate connection with the recent 

 experiments of Paschen and Back. Before entering 

 into theoretical speculation as to the probable origin 

 of the anomalous mode of separation, we think it 

 advisable to extend the investigation to see if such 

 an effect is common to satellites of lines of other 

 elements. H. Nagaoka. 



T. Takamine. 



Physical Institute, Imperial University, Tokvo, 

 July 31. 



The Piltdown Horse " Grinder." 



In the Dawson-Woodward paper on the Piltdown 

 skull of a " hominid " (Q.J.G.S., vol. lxix.) mention 

 is made of a tooth of Equus, and an accurate descrip- 

 tion (so far as it goes) is given. After handling it 

 again at Kensington, and comparing; it by measure- 

 ments with recent finds from this Stort Valley, also 

 with one recently placed in the Sedgwick Museum, 

 and another in the Saffron Walden Museum, I 

 have found that the tooth in question appears to be 

 the fourth premolar (p.m. 4) of Equus rohustus, which 

 Prof. Cossar Ewart has recognised as the true 

 " Solutr£ Horse" ("Restoration of an Ancient Race of 

 British Horses," Proc. Roy. Soc, Edin., vol. xxx., 

 part 4). The importance of this identification (if it 

 is confirmed by experts) is too obvious to need further 

 comment to those who are familiar with recent ad- 

 vances in our knowledge of the prehistoric horse. It 

 remains to determine the exact horizon in the gravel- 

 deposit at which this tooth was found before we can 

 appraise its precise value as a time-index (see Nature, 

 July 8, 1909, paper to the Royal Soc. bv Prof. J. C. 

 Ewart, F.R.S.). But one may venture to assert that 



NO. 2287, VOL. 91] 



the stratum of Piltdown gravel, from which this tooth 

 of Equus came, is of far later date than anything 

 belonging to the Pleiocene. A. Irving. 



Bishop's Stortford, August 16. 



Automatic Stability in Aeroplanes. 



Prof. Bryan's explanation of his model illustrating 

 instabilit) due to friction is somewhat obscure, but 

 in any case it is difficult to see how there is not a 

 violation of the principle of conservation of energy 

 in his conclusion. 



If 6 and ■£ are the angles made with the vertical 

 at any instant by OQ and OP respectively, the poten- 

 tial energy of the controlling mechanism is fc(9-<£)-, 

 where k is some constant. 

 When the system starts to 

 move from the position de- 

 picted in the figure, its 

 energy is C4-fe(/3-a) 2 , and 

 when it reaches the position 

 of rest on the other side its 

 energy is C'4-fc(7-a) 2 , 

 where C and C depend on 

 the position of Q and Q' 

 relative to O, and therefore 

 are equal, and and 7 de- 

 note the angles which OP 

 makes with vertical in the 

 first and last positions. Now 

 Prof. Bryan states that 7 is 

 greater than 0, in spite of 

 the fact that some energy has been degraded by 

 friction in passing from one position to the other. 

 Where is his concealed source of energy? 



. J. B. Dale. 



The system contemplated in my letter assumes the 

 existence of an external source of energy, and perhaps 

 it might have saved misunderstanding if this fact 

 had been stated at the expense of brevity. If we 

 imagine an aeroplane performing purely lateral oscil- 

 lations, and suppose it furnished with a pendulum so 

 arranged as to operate on a pair of ailerons, we have 

 a system the action of which might be represented to 

 a first approximation by the model assumed by 

 me. In this case the necessary energy is being 

 supplied by the wind, which, by its action on the 

 ailerons, causes the aeroplane to rotate like a wind- 

 mill during the interval that the pendulum rotates 

 with the aeroplane, while the inclinations of the 

 ailerons remain constant. The work done in a small 

 displacement is of the form k(Q—<t>)dd, but this does 

 not integrate into an expression representing "potential 

 energy. G. H. Bryan. 



Physiological Factors of Consciousness. 



I wish to ascertain the opinion of physiologists and 

 psycho-physicists on the following point, and I hope 

 some readers of Nature will be good enough to 

 supply me with the information required. 



My query is this : What is the true explanation of 

 the fact that stimuli sufficiently strong to arouse vivid 

 sensations in a subject while he is wide awake appar- 

 ently fail to arouse any sensation at all in a state of 

 unconsciousness? Four explanations appear to be pos- 

 sible, namely : — ■ 



(1) The afferent nervous current does not penetrate 

 at all along the conducting paths into the central 

 nervous system. 



(2) It penetrates into it, but only up to a little way, 

 and does not reach the highest nervous centres. 



