480 



ELECTRICITY. 



menu of 

 Hemmer. 



perspiration. " The electricity," he observes, " was 

 ometiiM* positive, and at other time* negative, with- 

 out my being able to ascertain the cause of these varia- 

 tions. It sometimes happened that the balls of the elec- 

 trometer separated and collapsed in succession, when, 

 being in* state of insulation, I made a great motion, and 

 kept one of my hand* applied to the electrometer. If, 

 for example, after having bent my body forwards, I 

 raised myself suddenly, F saw the balls diverge to a 

 considerable distance, and then collapse, unless when I 

 drew away my hand when they were in a state of di- 

 vergency,and then they continued in this state of diver- 

 gency, and exhibited positive electricity. The electri- 

 city which appears in these experiments is obviously 

 produced by the friction of the body against the clothes 

 which cover it The motion produced by respira- 

 tion is sufficient of 'itself to excite a little electricity, for 

 when a person remains upon the insulated stool in a 

 state of the most complete repose that can be observed 

 by a living being, sensible indications of electricity will 

 be exhibited, if the hand is laid for some time on one of 

 Volta's condensers. In order to succeed in these ex- 

 periments, the clothes of the person must be warm by 

 the heat of the body ; for whenever cold clothes are put 

 on, no electricity appears. The same thing takes place 

 when the body is covered with perspiration. It most 

 also be observed, that there are some individuals who 

 give no signs of electricity. The knowledge of spon- 

 taneous electricity is not a matter of indifference in me- 

 dicine ; for however weak it may be, the continuity of 

 its action ought necessarily to influence the animal eco- 

 nomy. Is it not, in part, this electricity which renders 

 moderate exercise, and clothes moderately warm and 

 dry, so favourable to insensible perspiration, and to all 

 the secretions of the human body i" These experiments 

 of Saussure were repeated with the same results by Vol- 

 ta, Landriani, and the Abbe Bertholon. 



The most successful experimenter, however, on this 

 branch of electricity was M. J. J. Hemmer, who has pub- 

 lished a full account of his experiments in the 6th vo- 

 lume of the Transactions of the Electoral Academy of 

 Sciences at Manheim. In order to examine the electri- 

 city of his own body, he insulated himself upon a board 

 supported by glass feet, and then touched for half a 

 minute or less, the plate of a condenser of his own 

 invention. The condenser was then applied to Ca- 

 vallo's electrometer, as improved by Saussure, and by 

 means of a glass tube rubbed with woollen cloth, he 

 examined the electricity of the diverging balls. His 

 experiments were made on the 21st February 1786, 

 and have since been repeated, both upon himself and 

 upon persons of various ages and constitutions, upon 

 persons in motion and at rest, dressed or undressed, fa- 

 tigued or in good spirits, hot or cold, fasting or full, and 

 sleeping or waking. The following are the principal 

 results obtained by Mr Hemmer. 



1 . The electricity of the human body is common to 

 all men, and it was found in 30 persons of all ages 

 and both sexes ; but in different persons it has different 

 degrees of strength, and is positive in some and nega- 

 tive in others. 



2. The strength and character of the electricity is often 

 different in the same person. In 2422 experiments, M. 

 Hemmer found it 1252 times positive, 771 times ne- 

 gative, and 399 times imperceptible. Out of 94 expe- 

 riments made upon his maid, it was 1 7 times positive, 

 S3 times negative, and 44 times imperceptible. 



3. Although the electricity often changes in the 

 course of the experiment, and even becomes impercep- 



tible, yet the electricity of the human body appear* 

 to be naturally positive ; for it always possesses this 

 kind of electricity when exposed to no violent exertion. 

 Out of 3.56 experiments made when be wa sitting at 

 rest, and when the natural heat of his body was not 

 disturbed, M. Hemmer rras 332 times in a state of 

 positive electricity, 1 \ times in a state of negative elec- 

 tricity, and 10 times the electricity of his body was not 

 perceptible. 



4. Cold changes the natural or positive electricity 

 into negative, or, at least, diminishes its intensity. Out 

 of 62 experiment* made upon himself, when be came 

 from a temperature of about 32 of Fahrenheit, his elec- 

 trity was 38 time* negative, 15 times positive, and 7 

 times imperceptible. 



5. Lassitude impedes the positive electricity of the 

 body, and changes it into the opposite. Out of 1C 

 times that he walked backwards and forwards in his 

 apartment, or was otherwise employed, Hemmer found 

 the electricity only once weakly positive, ten times ne- 

 gative, and fue times imperceptible. In 32 experiments 

 made when he was standing at rest, the electricity was 

 two times weakly positive, and 30 times impercepti- 

 ble. In 27 experiments when he sat at rest, it was al- 

 ways strongly positive ; and in five experiments when 

 walking at a gentle pace, it was perceptibly positive. 



6. The electricity of the body is changed into the op- 

 posite kind, by sudden, speedy, and violent motion. 



See Saussure, Journal de Paris, 1 7 8 1-, No. 101. Hem- 

 mer, Transactions of the Electoral Academy of Sciences 

 of Manheim, torn. vi. or Tilloch's Philosophical Ma- 

 gazine, vol. v. pp. 1, 140. Bertholon, De rElectricite 

 du Corns Humain, torn. i. p. 133, &c. ; and Part I. 

 Chap. I. Sect. I. of the present article. 



SECT. IX. On the Negative Electricity of Vitiated Air. 



THE production of negative electricity by the vitia- On thene- 

 tion of atmospheric air, was first observed by Mr John game eke. 

 Read of Knightebridge. Having often noticed that the nd*j of ri. 

 electricity of a small room in which he sat was negative, " ated *" 

 when that of the external air, and even that of the ad- 

 joining apartment, was positive, he began to suspect 

 that this difference was owing to the vitiation of the air 

 by respiration. In order to determine this point, he 

 invited a friend into his room on the 9th of July 1793, 

 when the weather was hot and serene, and the thermo- 

 meter at 75 ; and having shut up the doors and win- 

 dows, he placed himself nearly in the middle of the 

 room, and his companion at the side of it At the end 

 of 20 minutes, Mr Read was in a profuse perspiration, 

 and having worked the doubler, he found tie electricity 

 negative. He then examined the electricity of his bed- 

 room a little while before he went to rest, and found it 

 positive ; but when he rose at six o'clock next morning, 

 he found that it had become negatively electrified, in 

 a room which had been newly white washed and paint- 

 ed, and was therefore full of noxious effluvia, he also 

 found the electricity negative. 



Mr Read examined the electricity of the air in the 

 charity-school at Knightsbridge, when it was vitiated 

 by a great number of children, and he always found it 

 strongly negative, while the schoolmaster's parlour ad- 

 joining to it was in a positive state ; and on the 5th of 

 July, when the thermometer was at 76, Mr Read went 

 to the same school, but finding the doors and windows 

 open to admit fresh air, and experiencing no disagree- 

 able smell, he thought it unnecessary to make the ex- 

 periment The schoolmaster, however, remarked that 



