Dec. 19, 1889] 



NATURE 



155 



chloroform are death by stoppage of respiration and 

 death by stoppage of the heart ; " he lays as much stress 

 on the effect on the heart as on the respiration, and he 

 proceeds to affirm that too strong chloroform vapour 

 may very quickly paralyze the heart. This view is, in- 

 deed, similar to the one we have already mentioned as 

 taught in the London schools of medicine. It is also 

 well known that death may occur soon after chloroform 

 has begun to be administered, from the heart being 

 affected. If the operation is begun too soon, fainting 

 from pain may supervene, and a fatal result occur : this 

 has always been strongly insisted upon by Dr. Brunton. 

 Surgeon-Major Lawrie says that in such cases it is not 

 the chloroform that acts on the heart, but simply that 

 there is fatal syncope or fainting. 



From the large number of experiments on animals 

 which Dr. Brunton has performed in India, in conjunc- 

 tion with the Hyderabad Commission and a medical 

 delegate of the Indian Government, it appears that the 

 " danger from chloroform is asphyxia or an overdose ; " 

 there is none whatever from the heart direct. This state- 

 ment is a distinct reversal of the view generally held in 

 England. It means that chloroform causes a fatal result 

 by affecting the respiration or by too much being taken 

 into the system and affecting the brain ; and that there 

 is no direct paralysis of the heart from the chloroform. 

 A perfectly impartial opinion cannot, however, be formed 

 from the scanty records of the investigation which have 

 been as yet received in England. We must wait for 

 fuller details of the experiments before a final judgment 

 can be passed. 



It is well, however, to point out that the prevailing view 

 in England has been founded, not only on experiments on 

 the lower animals, but also on the extended clinical ob- 

 servation of two generations of medical men. Clinical 

 observation is not so accurate or so lucid as that of direct 

 experiment, but it has its value, and one by no means to 

 be despised in a case where it is so extensive, and 

 directed to a subject of such great importance, not only 

 to the medical profession, but to the general public, as 

 the question of the administration of chloroform. 



ON THE CA VENDISH EXPERIMENT. 



T N the last number of the Proceedings of the Royal 

 -*■ Society (vol. xlvi. p. 253), I have given an account of 

 the improvements that I have made in the apparatus of 

 Cavendish for measuring the constant of gravitation. 

 ■As the principles and some of the details there set out 

 apply very generally to other experiments where extremely 

 minute forces have to be measured, it is possible that an 

 abstract of this paper may be of sufficient interest to find 

 a place in the columns of Nature. 



In the original experiment of Cavendish (Phil. Trans., 

 1798, p. 469), as is well known, a pair of small masses, 

 mm (Fig. i), carried at the two ends of a very long but 

 light torsion rod, are attracted towards a pair of large 

 masses, M M, thus deflecting the arm until the torsion of 

 the suspending wire gives rise to a moment equal to that 

 due to the attraction. The large masses are then placed 

 on the other side of the small ones, as shown by the 

 dotted circles, and the new position of rest of the torsion 

 arm is determined. Half the angle between the two 

 positions of rest is the deflection produced by the attract- 

 ing masses. The actual force which must be applied to 

 the balls to produce this deflection, can be directly 

 determined in dynamical units when the period of oscilla- 

 tion and the dimensions and masses of the moving parts 

 are known. In the original experiment of Cavendish, 

 the arm is 6 feet long, the little masses are balls of lead 

 2 inches in diameter, and large ones are lead balls i foot 

 in diameter. Since the attraction of the whole earth on 

 the smaller balls only produces their weight, i.e. the force 



with which they are attracted downwards, it is evident 

 that the balls, M M, which are insignificant in com- 

 parison with the size of the earth, can only exert 

 an extremely feeble attraction. So small is this that it 

 can only be detected when the beam is entirely inclosed 

 in a case to protect it from draughts ; when, further, the 

 whole apparatus is placed in a room into which no one 

 must enter, because the heat of the body would warm the 

 case unevenly, and so set up air currents which would 

 have far more influence than the whole attraction to be 

 measured ; and when, finally, the period of oscillation is 

 made very great, as, for instance, five to fifteen minutes. 

 In order to realize how small must be the force that will 

 only just produce an observable displacement of the 

 balls, mm^ it is sufficient to remember that the force 

 which brings them back to their position of rest is the 

 same as the corresponding force in the case of a pendulum 

 which swings at the same rate. Now a pendulum that 

 would swing backwards and forwards in five minutes would 

 have to be about 20,000 metres long, so that in this case 

 a deflection of one millimetre would be produced by a 

 force equal to 1/20,000,000 of the weight of the bob. In 

 the case of a pendulum swinging backwards and for- 

 wards once in fifteen minutes the corresponding force 

 would be nine times as small, or 1/180,000,000 of the 

 weight. 



In spite of the very small value of the constant of 

 gravitation, Cavendish was able, by making the appa- 

 ratus on this enormous scale, to obtain a couple which 



Fig. I. 



would produce a definite deflection against the torsion of 

 his suspending wire. 



These measures were repeated by Reich {Comptes 

 rendus, 1837, p. 697), and then by Baily {Phil. Mag., 1842, 

 vol. xxi. p. 1 1 1), who did not in any important particular 

 improve upon the apparatus of Cavendish, except in the 

 use of a mirror for observing the movements of the 

 beam. 



Cornu and Bailie {Comptes rendus, vol. Ixxvi. p, 954, vol. 

 Ixxxvi, pp. 571, 699, looi) have modified the apparatus 

 with satisfactory results. In the first place they have 

 reduced the dimensions of all the parts to about one- 

 quarter of the original amount. Their beam, an aluminium 

 tube, is only ^ metre long, and it carries at its ends 

 masses of \ pound each, instead of about 2 pounds, as 

 used by Cavendish. This reduction of the dimensions 

 to about one-quarter of those used previously is con- 

 sidered by them to be one of the advantages of their 

 apparatus, because, as they say, in apparatus geometri- 

 cally siniilar, if the period of oscillation is unchanged, 

 the sensibility is independent of the mass of the sus- 

 pended balls, and is inversely as the linear dimensions. 

 I do not quite follow this, because, as I shall show, if all 

 the dimensions are increased or diminished together, the 

 sensibility will be unchanged. If only the length of the 

 beam is altered and the positions of the large attracting 

 masses, so that they remain opposite to, and the same 

 distance from, the ends of the beam, then the sensibility 

 is inversely as the length. This mistake — for mistake it 

 surely is — is repeated in Jamin's " Cours de Physique," 

 tome iv. ed. iv. p. 18, where, moreover, it is emphasized 

 by being printed in italics. 



The other improvements introduced by Cornu and 



