Benjamin Franklin Papers

To Benjamin Franklin from Timothy Lane, 15 October 1766

From Timothy Lane1

Copy:2 The Royal Society

[Aldergate-Street,] October [15,] 17663


Being employed in some Electrical Enquiries about the beginning of the year 1762 it occured to me, that many Experiments on this Subject might be made with a much greater degree of precision if we could determine with any tolerable accuracy the comparative quantity of Electric Fluid, with which for any given Experiment, the Coated Phial is impregnated.

An In[s]trument, which I have contrived for this Purpose, may not improperly be called an Electrometer. I have herewith sent you a drawing thereof,4 with the Machine* to which it is fixed.

Fig 1.

A The Cylindrical Glass of the Machine used instead of a Globe.
The Cylindrical part of the Glass is 6 inches in lenth and 16 in circumference.5
B The Wheel at every turn of which the Cylindrical Glass revolves 4 times.
C The Conductor
D The Coated Phial
E a Brass Wire Loop, passing through the wood work to a Tin Plate on which the Coated Phial stands
F The Pillar of the Electrometer made of Wood bored cylindrically about ? of its lenth and rendred Electrical6 by being long baked in an oven and then boiled in Linseed Oil and again baked.
 At first the Pillar was made of Brass which tho it served very well to determine the Electric Stroke for Medical purposes, yet was defective in many Experiments, as the Table thereby became a ready Conductor.
G. Brass Work, having its lower part inclosed within the Bore of the Pillar
H. a Screw which passes through the Brass Work near the Bottom and fixes it in the Pillar
I a Groove for the Screw H to move in when the Electrometer is moved higher or lower, as the different hights of different Condensing Phials may require.
K a well polished haemispherical piece of Brass fixed to the Conductor
L a Steel Screw passing through the Top of the Brass work, whose threads are distant nearly 1/24 of an Inch from each other.
M a well polished spherical piece of Brass fixed to the Screw L and opposite to K. As the polish of K and M will often be destroyed by large Electrical explosions, the Polish should again be restored, particularly where the Expe[riments] require accuracy.
N a Scale with divisions equal to each turn of the Screw.
O a Circular Plate fixed to and moving with the Screw, pointing at each turn to the Division upon the Scale. This Plate is also divided into 12 to denote the parts of each Turn.

The Principle on which the Electrometer acts, is very simple, being merely this. The Coated Phial is hereby rendred incapable of accumulating and retaining any more than a certain quantity of the Electric Fluid, for any intended Experiment when a Metallic or Non Electric communication is made from the Screw H to the wire loop E of the Machine. And that quantity will be proportionate to the distance of K and M from each other, and consequently the Explosion and stroke will thereby be regulated.

Thus if a Person holds a wire fastened to the Screw H in one hand, and another Wire fixed to the Loop E in the other, he will perceive no Stroke, if K and M are in contact notwithstanding the Cylindical Glass A acts strongly. But if by turning the Screw L. the Ball M is distant from K 1/100 part of an Inch a very small stroke will be perceived, with an Explosion from K to M, and if K and M are distant one inch from each other, the quantity of the Electric Fluid, at the time of the Explosion will be increased 100. times. For example it appears by Experiment that if the Explosion happens after 4 Turns of the Wheel B. when M is distant from K 1/24 of an Inch or 1 turn of the Screw, the same will happen at 8 turns of the Wheel when M and K are distant 2 turns of the Screw or 1/12 of an Inch. And if K and M are distant 3 turns of the Screw, the turns of the Wheel will be twelve at the time of the Explosion, the same proportion will continue so far as the distance K and M is equal to the condensing Power of the Coated Phial without wasting. By wasting I mean when the Phial is so fully charged that part of the Electric Fluid escapes from the mouth of the Bottle, or from the Conductor into the air or to some adjacent non Electric.

The Number of Turns of the wheel, when K and M are at any of the above distances, will be more or less in proportion to the state of the Air, the Cylindrical Glass, the Cushion against which the Glass is rubbed, or the Coated Phial which last will not give so great an explosion when the Air is damp as when dry.

The fewer the Number of Turns of the wheel at any given distance, the better the Machine worketh. Thus a Comparative difference between any two Machines may be determined.

A Wire in general is better than a Chain, unless the Chain is held very tight, particularly in very small Strokes the Electric fluid will be lost in passing from Link to Link of the Chain. By Experiment it also appears, that the quantity of Electric Fluid at every Explosion will be proportionate to the quantity of Coated Glass, either as to the size of the Coated Phial or to the Number of Phials added. For Example. If the Phial D has half of the Coating on each side of the Glass taken off the Explosion will happen after half the Number of Turns of the Wheel, at any of the above distances and if a Phial with twice the quantity of Coated Glass, is employ’d instead of D, the turns of the Wheel will be double the same will happen if two Coated Phials each equal to D are used, and if three Phials the Number of Turns will be triple &c.

The Phial D used in the following Experiments contains about 80 Square inches of Coating on the inside and also on the outside of the Glass, the mouth being stopped with wood prepared like the Pillar and the Coating not so near the mouth of the Phial as usual to prevent7 the Electric Fluids wasting, and thereby the Phial may be more fully charged.

As K is part of the Conductor and M of the Electrometer, the distance between them is the distance of the Electrometer from the Conductor, whence it will be readily understood, when I relate the distance of the Electrometer in any Experiments for Example. The Electrometer at 20, that is M is 20 turns of the Screw distant from K or 20/24 of an Inch.

That Lightening and Electricty are of very near affinity, if not the same, evidently appears from the many discoveries you have made. And as the following Experiments tend to confirm the same as well as to illustrate the use of the Electrometer I hope they will not be unacceptable.

Experiment i. A Peice of Moist Tobacco Pipe Clay rolled cylindrically, a. Fig 2. about an inch in lenth and about 2 or 3/10ths of an inch in diameter, having a Peice of Wire thrust into each end bb, distant from each other about 1/10 of an Inch with the solid Clay between and the end of one of the Wires cc fixed to the Loop of the Machine E and the other fixed to the small Screw of the Electrometer H will with an Explosion at 20 of the Electrometer, be inflated as in Fig. 3, or if the Clay is too dry or the quantity of Electricity too great, it will burst in Peices leaving only the Clay concave near the ends of the Wires. And tho the Experiment will in appearance differ, yet it will always leave evident signs of an Explosive Power or sudden rarefaction, excepting when the wires in the Clay are at too great a distance from each other, then the Electric Fluid will only run over its moist surface. If instead of Clay a Mucilagenous vegetable paste is used, as wheat flower and Water &c. the Experiment will appear the same.

Experiment 2. A peice of common hard baked smoaking Tobacco Pipe about an inch in lenth with the bore in the Middle filled with Clay and Wires put into each end as in Fig 2 and applied in the same manner to the Machine will burst into many peices, at 20 of the Electrometer, sometimes the peices will be driven near ten feet from the Machine.

Experiment 3. A small Square peice of Portland Stone with holes drilled at each end so as to admit the wires, was in like manner burst in peices, when a second Coated Phial was added to increase the Stroke.

The Iron cramps in stone Buildings are similar to the Wires, and when a Building is struck by Lightening produces a similar effect. I observed that when the Tobacco Pipe or stone was damp the Experiment succeeded better than when dry, and I frequently found that either of them after being first dipped in Water would be broken with a less explosion than before.

This observation, is different from the received opinion of many, not well acquainted with Electricity, that Lightening is less likely to do mischeif after a Shower of Rain than before. So far may be true that the Rain will bring down some of the Lightening, and also render Thatched Houses &c. less likely to take fire; but will not assist Buildings that have Metallic Ornaments near their Tops, as the Weather Cocks of Churches &c. As a metallic Conductor from the Tops of Buildings to the Earth will prevent the effects of Lightening on them, so will the smallest wire prevent the effects of Electricity on the Stone or Tobacco Pipe when in contact with the two wires cc. Fig 2.

If the Tobacco Pipe instead of Clay is filled as above with an Electric Substance as Wax, Powderd Glass or with any non Electric substance inferior to Metals as a Conductor, it will be burst in Peices, with nearly the same quantity of the Electric Fluid.

As the above Experiments succeeded better when the Stone or Clay were previously dipped in Water than before, I was induced to try Water only.

Experiment 4. Having made a hole without any cracks on the side thro the bottom of the Phial a Fig 4, which may easily be done if the Phial is conical at the bottom as in the Figure, by holding the Phial inverted in one hand and with the other strikeing a Pointed Steel Wire against the Apex of the Cone.

Through this hole I passed a Wire b. and filled the bottom c with melted Sealing Wax leaving the other end of the Wire out at d. When the Wax was cold, the Phial was about ¾ ths filled with water, and stopped with a Cork thro which a Wire e. was passed downwards, till the Points of the two wires were distant from each other about 1/10 of an Inch as near as my Eye could determine: a Wire from the Electrometer was fixed to e and another from the Loop of the Machine was fixed at d. By an Explosion, at 20 of the Electrometer, the Phial burst in peices, the Top falling from the Bottom near the point of the lower Wire. Another Phial was fitted in the same manner and the Cork cut longitudinally that the air might freely pass at the time of the Explosion, but this made no sensible difference. Often times the Phial is so cracked as to resemble Radii from a Center.

If Oil is used instead of water, the Event will be the same.

The quantity of Electricity necessary to burst the Phial; appears to vary more in proportion to its thickness than its size. Many Phials of various sizes may be broken at 10 of the Electrometer while others nearly of the same size remain sound with a Stroke at 30 or even more.

I generally found Green Glass more difficult to break than white.

When the Phial is not broken by the Electric Stroke, the agitation of the Water may be sensibly observed at the instant of the Explosion, and the Electric Spark evidently seen to pass through the water from the point of one wire to the other.

This remarkable appearance of the Electric fluids passing through water may be observed, when the Electrometer is at a smaller distance from the Conductor, if the wires are nearer to each other.

I have broken many Phials by the Electric Strokes as above mentioned when the wires have been at the various distances, of above one inch to 1/20 of an inch from each other, as near as my Eye could determine. But the distance of about 1/10 of an Inch I usually prefer. The above experiments I have often repeated and may therefore be relied on: Want of leisure has prevented me from pursuing them more minutely. But I hope they will serve as hints to others of more abilities and leisure than Your respectfull Humble Servant

[T Lane]8

1On Timothy Lane, member of the Apothecaries’ Company and electrical experimenter, see above, p. 288 n. His inventive ability, demonstrated in this paper, appeared again in his creation of the Patent Graduated Measures, “which have proved very efficacious in preventing venders and purchasers from being deceived by such false measures as were detected by the Censors of the Royal College of Physicians in the years 1800 and 1801.” Gent. Mag., lxxvii (1807), 689.

2This copy is in a set of relatively small pages stitched together, apparently in Lane’s hand and apparently sent to the Royal Society to be used as printer’s copy. The text appears on the right-hand pages, the left pages being reserved for additions to be inserted at points indicated by carets in the text. The letter was printed in Phil. Trans., lvii (1767), 451–60. An occasional doubtful word has been supplied from the printed text. The paper was reprinted as a separate pamphlet in 1768. The cover page of the ms is marked “Received Aug. 1767” and “To Benjamin Franklin LLD. FRS,” and carries in another hand a description of the contents.

3The material in brackets does not appear in the ms but is supplied from the printed text.

4Lane’s original drawing does not survive. The illustration printed here is reproduced from Tab. xx, in Phil. Trans., lvii, facing p. 451, the first page of the printed text.

5Elements A, B, C, and D, as described here and shown on the plate, were merely one form of the familiar device by means of which frictional electricity was generated by revolving wheel B, and thereby cylindrical glass A, and was then transferred via conductor C to phial (or Leyden jar) D. The wire loop E was the only special feature of this assembly. The elements lettered from F through 0 constituted the electrometer proper.

6That is, rendered non-conducting.

7Phil. Trans. reads here: “and the coating not too near the mouth of the phial, to prevent” etc.

8The signature, not on the ms, is supplied from Phil. Trans.

Authorial notes

[The following note(s) appeared in the margins or otherwise outside the text flow in the original source, and have been moved here for purposes of the digital edition.]

º *This Portable Machine is the contrivance of Mr. Read Mathematical In[s]trument Maker at Knight[s]brid[g]e near London.

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