May 5, 1870] 
MATURE 
17 
‘obtained by Camera Lucida outline drawings of a given scale. 
On a Cause of Error in Electroscopic Experiments.” By 
Sir Charles Wheatstone, F.R.S. 
_ Toarrive at accurate conclusions from the indications of an 
electroscope or electrometer, it is necessary to be aware of all 
the sources of error which may occasion these indications to be 
misinterpreted. In the course of some experiments on electrical 
‘conduction and induction which I have recently resumed, I was 
“frequently delayed by what at first appeared to be very puzzling 
‘results. Qccasionally I found that I could not discharge the 
electrometer with my finger, or only to a certain degree, and that 
“it was necessary, before commencing another experiment, to 
“place myself in communication with a gas-pipe which entered 
‘the room. TElow I became charged I could not at that time 
explain ; the following chain of observations and experiments, 
however, soon led me to‘the true solution. I was sitting at a 
fable not far from the fireplace, with the electrometer (one of 
Peltier’s construction) before me, and was engaged in experi- 
menting with disks of various substances. To ensure that 
the one I -had in hand, which was of tortoise-shell, 
‘should be perfectly dry, I rose and held it for a minute 
before the fire; returning and placing it on the plate of 
the electrometer, I was surprised to find that it had apparently 
acquired a strong charge, deflecting the index of the electro- 
meter beyond go”. I found that the same thing took place with 
every disk I thus presented to the fire, whether of metal or any - 
other substance. My first impression was that the disk had 
been rendered electrical by heat, though it would have been 
extraordinary that, if so, such a result had not been observed 
before ; but on placing it in contact with a vessel of boiling 
water, or heating it by a gas-lamp, no such effect was produced. 
I next conjectured that the phenomenon might arise from a 
difference in the electrical state of the air in the room and at the 
top of the chimney ; and to put this to the proof, I adjourned to 
the adjacent room where there was no fire, and bringing my 
disk to the fireplace I obtained precisely the same result. That 
this conjecture, however, was not tenable was soon evident, be- 
cause I was able to produce the same deviation of the needle of 
the electrometer by bringing my disk near any part of the wall 
of the room. This seemed to indicate that different parts of the 
yoom were in different electrical states ; but this again was dis- 
proved by finding that when the positions of the electrometer 
and the place where the disk was supposed to be charged were 
interchanged, the charge of the electrometer was still always 
negative. The last resource was to assume that my body had 
become charged by walking across the carpeted room, though 
the effect was produced even by the most careful treading. This 
ultimately proved to be the case; for resuming my seat at the 
table and scraping my foot on the rug, I was able at will to 
move the index to its greatest extent. 
Before I proceed further I may state that a gold-leaf electro- 
meter shows the phenomena as readily. When I first observed 
these effects the weather was frosty; but they present them- 
selves, as I have subsequently found, almost equally well in all 
states of the weather, provided the room be perfectly dry. I 
will now proceed to state the conditions which are necessary for 
the complete success of the experiments, and the absence of 
which has prevented them from being hitherto observed in the 
striking manner in which they have appeared to me. The 
most essential condition appears to be that the boot or shoe of 
the experimenter must have a thin sole and be perfectly dry; a 
surface polished by wear seems to augment the effect. By 
rubbing the sole of the boot against the carpet or rug, the elec- 
tricities are separated, the carpet assumes the positive state and 
the sole the negative state; the former being a tolerable insu- 
lator, prevents the positive electricity from running away to the 
earth, while the sole of the foot, being a much better conductor, 
readily allows the charge of negative electricity to pass into the 
body. So effective is the excitation, that if three persons hold 
each other by the hands, and the first rubs the carpet with his 
. foot while the third touches the plate of the electrometer with 
his finger, a strong charge is communicated to the instrument. 
Eyen approaching the electrometer by the hand or body, it 
becomes charged by induction at some distance. 
A stronger effect is produced on the index of the instrument if, 
_ after rubbing the foot against the carpet, it be immediately raised 
from it. When the two are in contact, the electricities are in 
some degree coerced or dissimulated ; but when they are sepa- 
rated, the whole of the negative electricity becomes free and ex- 
pands itself in the body, A single stamp on the carpet followed 
by an immediate removal of the foot causes the index of the elec- 
trometer to advance several degrees, and by a reiteration of such 
stamps the index advances 30° or 40°. The opposite electrical 
states of the carpet and the sole of the boot were thus shown : 
after rubbing, I removed the boot from the carpet, and placed 
on the latter a proo&plate (¢.e. a small disk of metal with an in- 
sulating handle), and then transferred it to the plate of the elec- 
trometer : strong positive electricity was manifested. Performing 
the same operation with the sole of the boot, a very small charge 
was carried, by reason of its ready escape into the body. The 
negative charge assumed by sole-leather when rubbed with ani- 
mal hair was thus rendered evident. I placed on the plate of the 
electrometer a disk of sole-leather and brushed it lightly with a 
thick camel’s-hair pencil ; a negative charge was communicated 
to the electrometer, which charge was principally one of conduc- 
tion, on account of the very imperfect insulating power of the 
leather. Various materials, as India-rubber, gutta-percha, &c., 
were substituted for the sole of the boot ; metal plates were also 
tried; all communicated negative electricity to the body. 
Woollen stockings are a great impediment to the transmission of 
electricity from the boot ; when these experiments were made I 
wore cotton ones. When I substituted for the electrometer a 
long wire galvanometer, such as is usually employed in physio- 
logical experiments, the needle was made to advance several 
degrees. 
At the meeting of the British Association at Dublin in 1857, 
Professor Loomis, of New York, attracted great attention by his 
account of some remarkable electrical phenomena observed in 
certain houses in that city. It appears that in unusually cold 
and dry winters, in rooms provided with thick carpets and heated 
by stoves or hot-air apparatus to 70°, electrical phenomena of 
great intensity are sometimes produced. A lady walking along 
a carpeted floor drewa spark one quarter of an inch in length be- 
tween two metal balls, one attached to a gas-pipe, the other 
touched by her hand; she also fired ether, ignited a gaslight, 
charged a Leyden jar, and repelled and attracted pith-balls 
similarly or dissimilarly electrified. Some of these statement 
were received with great incredulity at the time both here and 
abroad, but they have since been abundantly confirmed by the 
Professor himself and by others. (See Silliman’s American 
Journal of Science, July 1858.) 
My experiments show that these phenomena are exceptional 
only in degree. The striking effects observed by Professor Loo- 
mis were feeble unless the thermometer was below the freezing- 
point, and most energetic when near zero, the thermometer in 
the room standing at 70°. Those observed by myself succeed in 
almost any weather, when all the necessary conditions are ful- 
filled. Some of these conditions must frequently be present, and 
experimentalists cannot be too much on their guard against the 
occurrence of these abnormal effects. I think I have donea 
service to them, especially to those engaged in the delicate inves- 
tigations of animal electricity, by drawing their attention to the 
subject. 
Royal Institution, May 2. Annual meeting.—Sir Henry 
Holland, Bart, M.D., D.C.L., F.R.S., President, in the chair. 
The annual report of the Committee of Visitors for the year 
1869 was read and adopted. The books and pamphlets pre- 
sented in 1869 amounted to 255 volumes, making, with those 
purchased by the managers, a total of 388 volumes added to the 
library in the year, exclusive of periodicals. Forty-seven new 
members were elected in 1869. Sixty-three lectures and nine- 
teen evening discourses were delivered during the year 1869. 
The following gentlemen were unanimously elected as officers 
for the ensuing year :—President : Sir Henry Holland, Bart., 
M.D., D.C.L., F.R.S. Treasurer: William Spottiswoode, 
age F.R.S. Secretary: Henry Bence Jones, M.A.,,M.D., 
~RAS. 
Royal Geographical Society, April 25.—Sir R. IL 
Murchison, Bart., President, in the chair. The following 
new Fellows were elected :—Baron Osten Sacken, Secretary to 
the Imperial Geographical Society, St. Petersburg (Hon. 
Corresponding Member) ; Thomas M. Blackie; Lieutenant 
Evelyn Baring, R.A. ; Colonel Shuckburgh Denniss; George B. 
Hudson ; Lord Lawrence, G.C.B.; and John Fenton Taylor. 
A paper was read, entitled “ An Expedition to the Trans- 
Narym Country,” by Baron Osten Sacken. This paper, which 
had been translated from the Russian by Mr. Delmar Morgan, 
contained a narrative of a journey, undertaken for the purpose 
of a reconnaissance survey, by General Poltoratsky, across the 
