Feb. 18th. 1854.
My dear Tom
I have written to Ruhmkorff,1 but you must not calculate on moving the instrument2 in less than a month. I think it well to mention this lest you should build upon it for your lectures. The following are one or two experiments: – first to shew the bending of your compound bar3 by unequal expansion.
one
one end of the bar rests on a plate of metal on the black B. By bending the middle touches the metal rod C D and thus closes a galvanic circuit4 the moment the circuit is closed the platinum lamp5 [P] which can be placed at some distance from the table glows, G is the battery.
The same lamp may be used to shew expansion two stands A B are set so that a bar C nearly fills the space between them. By heating it does fill the space. Make A B close a galvanic circuit in which the little lamp is introduced.
To shew expansion of gases I have made use of current also. By sending a current through the bulb coil is heated the air expands and is transferred to the tube T which was previously filled by a coloured liquid. To shew currents of air bend a thin glass tube say an inch in diameter heat with a spirit lamp6 at A – the current ascends – a smoky taper7 placed at B has its smoke drawn upwards at C it is sucked downwards and traverses the entire tube.
The bursting of iron bottles by freezing is also a very good experiment. I burst two in my lecture on the subject.8
A balloon of heated air is also a popular experiment.
A Smeaton’s pyrometer9 shews the expansion of bodies for a popular audience very well.
Find out for me wherein Bulloughs patent10 for throwing will work out of gear when a thread breaks consists. Edmondson knows all about it – I did know but have forgotten it – let me have this intelligence if you can by Tuesday morning.
Affectionately | John
RI MS JT/1/HTYP/314
LT Typescript Only
I have written to Ruhmkorff: letter missing.
the instrument: possibly Ruhmkorff’s induction coil (see letter 0864, n. 1).
compound bar: a bar composed of two types of metals, which can be used to show the unequal expansion of differing metals when heated.
a galvanic circuit: ‘a current generated by chemical action and coming directly from the cell, pile, or battery in which it is generated’ (G. M. Beard and A. D. Rockwell, On the Medical and Surgical Uses of Electricity, 8th edn [New York: William Wood & Company, 1892], p. 777).
platinum lamp: ‘an electric lamp in which the filament is made of platinum’ (OED).
spirit lamp: ‘a lamp fed by methylated or other spirits, and used esp. for heating, boiling, or cooking’ (OED).
taper: a candle made of wax (OED).
my lecture on the subject: not identified.
Smeaton’s pyrometer: An instrument developed by the English civil engineer John Smeaton (1724–92), which was used to measure the expansion of materials when subject to heat and cold (J. Smeaton, ‘A Description of a New Pyrometer, with a Table of Experiments Made Therewith’, Phil. Trans. 48 [January 1753], pp. 598–613).
Bulloughs patent: In 1841, John Bullough (1836–91), a manufacturer of textile machinery, patented the weft fork; the invention prevented cloth damage by stopping the loom when the thread broke (ODNB).
Please cite as “Tyndall0884,” in Ɛpsilon: The John Tyndall Collection accessed on