132 



NATURE 



{Jtme 17, 1875 



rapidity is attained, after which little^ further change 

 occurs. 



An interesting experiment may be made with these 

 machines, which illustrates a well-known dynamical prin- 

 ciple, by turning the machine at a steady rate, with the 

 wires for transmitting the current disconnected, and 

 observing the great additional force required to maintain 

 the motion on connecting the wires. 



The machine may be converted into an electro-mag- 

 netic one by transmitting the current from a voltaic pile 

 through the helices of the iron ring, which will then rotate 

 upon its axis. If the current be supplied by another 

 magneto-electric machine, the same result will be pro- 

 duced, and we shall thus have mechanical force, after 

 assuming the form of current electricity, reappearing, but 

 with some loss, in the form of mechanical force. In an 

 experiment on the large scale described by M. Breguet, 

 the loss amounted only to thirty per cent. If during this 

 experiment the machine which supplies the current has 

 its motion reversed, the other machine will soon come to 

 rest, and afterwards begin to turn in the opposite direc- 

 tion. The intensity of the current, M. Breguet remarks, 

 augments with the velocity of the rotation, the electro- 

 motive force having been proved by experiment to be 

 proportional to the velocity. At first view it might appear 

 that the resistance would remain constant ; but as the 

 intensity is found not to be proportional to the velocity 

 of an invariable circuit, we are led to the conclusion 

 that the resistance of the machine is not constant. This 

 important point has been established by M. Sabine, but 

 the details of his experiments have not been published. 

 The increase of resistance is, however, so small, that a 

 machine which gives with a velocity of 100 turns per 

 minute a current equal to that of one small Bunsen's 

 element, will give with a double velocity a current equal 

 to two such elements a little larger, and with a quadruple 

 velocity a current equal to four still larger elements of 

 Bunsen. It is certain that this increase of electromotive 

 force cannot be indefinite, but must tend towards a limit ; 

 but this limit does not appear to have been reached even 

 with a velocity of 3,000 turns per minute. 



{To be continued^ 



ON THE TEMPERATURE OF THE HUMAN 



BODY DURING MOUNTAIN-CLIMBING 

 T N the year 1869 both Dr. Wm. Marcet, of Nice,* and Dr. 

 ■•■ Lortet, of Lyons,f published the results of thermo- 

 metric experiments prosecuted by themselves on them- 

 selves during the ascent of Mont Blanc. Both physio- 

 logists discovered that during the act of ascent, if it were 

 rapid and prolonged for any considerable time, the tem- 

 perature of the body fell considerably, as much as 3"6° F. 

 in the case of the English, and even 8*6° F. of the French 

 observer. The temperature was taken in the mouth, and 

 read off by means of a small reflector attached to the 

 thermometer, which is a much more satisfactory manner 

 of recording reducing temperatures than the employment 

 of maximum registering instn.iments. Dr. Marcet tells 

 us that in order to assure himself that the cooling of the 

 body during the ascent was really due to the muscular 

 effort, and not to the effect of the rarefaction of the air, 

 he made one ascent (from Cormayeur to the plateau of 

 Mont-Frety, about 2,440 yards high) partly on mule-back. 

 After having gone two-thirds the distance, his tempera- 

 ture was 97*5° F., when, leaving the mule, he performed 

 the rest of the journey on foot as quickly as possible. 

 Just before arriving at the end, his temperature was not 

 above 95° F., or 2-5° below what it was thirty-five minutes 

 before, at the lower level. Another peculiarity observed 

 by this author is that the body-temperature, after having 



sene, t. xxxvi. 



* " Archives des Sciences Physiques et Naturelles.' 

 p. 247. (Geneva. 



t " Recherches Physiologiques sur le Climat des Montagnes" (Paris.) 



diminished during an ascending walk, rapidly rose again 

 upon rest being taken, or on the speed being reduced. 



All these unexpected results have, from the absence of 

 fresh facts to throw light upon them, been but little dis- 

 cussed. It has been asked whether the above-described 

 fall of temperature depends on the transformation of the 

 energy of muscular action into work instead of, as usual, 

 into heat in the body. The answer to this question is, 

 however, not so easy as it might at first sight appear. If 

 the exalted temperature of warm-blooded animals in a 

 state of rest is the index of the amount of internal work 

 done by the heart and the respiratory muscles, then extra 

 muscular work will produce a proportionately greater rise 

 of body-temperature, as it is employed in doing less ex- 

 ternal work, and the reverse ; from which consideration 

 it is rendered theoretically probable that the rise in tem- 

 perature attending a rapid ascent of an incline would be 

 much less considerable than that accompanying a similar 

 effort which is attended by no external effect. In fact, the 

 temperature of an individual in the act of throwing 

 oranges forcibly away in all directions should be scarcely 

 above the normal, whilst if he continually throws one up, 

 again catching it, his temperature should rise consider- 

 ably. In the one case the muscular effort is employed in 

 heating the ground against which the moving oranges 

 come in contact whilst being brought to rest ; in the 

 other case the energy lost to the body in the upward pro- 

 jection of the mass is regained in the form of heat when 

 the muscles of the limbs resist its downward movement 

 in catching it. 



At this stage of the inquiry the elaborate investigations 

 of Prof Forel, of Lausanne,* prosecuted with indefati- 

 gable industry during the last four years, form an impor- 

 tant addition to the literature of the subject. This 

 physiologist, in a most painstaking and thorough manner, 

 has investigated the whole problem, together with all the 

 minor details associated with it : the results he has 

 arrived at have consequently a wider interest than the 

 simple solution of the question which originally led to 

 their being commenced. 



In his earlier series of experiments. Dr. Forel, whilst 

 staying at the Rhone Glacier, at Zermatt and at the Lake 

 of Geneva, ascended the Grimsel, the Riffel, and to 

 Chigney, as well as to other neighbouring heights, in the 

 end arriving at the following conclusions :— firstly, that the 

 method of measuring the body-temperature in the mouth 

 is not sufficiently precise for the study of the influence of 

 muscular exercise on the general temperature of the body ; 

 and, secondly, that the act of ascending normally pro- 

 duced an elevation of the temperature of the body to the 

 extent of several tenths of a degree, which diminishes 

 during the subsequent repose, in tending to regain the 

 normal standard. 



These results, obtained in 1871, being directly at 

 variance with those of Doctors Marcet and Lortet, Dr. 

 Forel repeated his experiments with greater precision 

 during the years 1873 and 1874. He commenced by 

 determining the relative values of the different regions of 

 the body in which it is possible to employ the thermo- 

 meter for the estimation of the general temperature. 

 More than a hundred observations in the floor of the 

 mouth led him to reject that position for the thermometer, 

 chiefly because it is next to impossible, during muscular 

 exercise, to retain the mouth closed for any considerable 

 time in a cold, dry, rarefied air. The palm of the hand, 

 the arm-pit, and the external auditory meatus were re- 

 jected as being even less advantageous. The rectum was 

 the last resource, and its advantages were found to be so 

 great that all the most important results, to be mentioned 

 directly, were arrived at from temperatures obtained in 

 that situation. 



The author commenced by forming a curve which repre- 



* "Experiences sur la Temperature du corps Humain danS I'acte de 

 I'ascension sur les Montagnes." (Geneva and Bale, 1871 and 1874.) 



