Faraday to John Peter Gassiot   17 January 1854

Three long bands of fine oiled silk crape (each being effectively a plate of fine dry oil - impervious & insulating.) respectively 108 inches long and 6 1/2 inches wide[.]

Two similar bands of tin foil each 106 or 107 inches long and only 6 inches wide[.]

so that the oiled silk shall overlap the edges of the tin foil[.]

The compound band is then bent backwards and forwards thus

so as to make a packet 6 1/2 inches wide & 18 inches long which lies in the bottom of the box and yet is equivalent to 702 square inches of doubly coated surface or a square of 25 inches in the side - the induction being through a thickness no more than that of one oiled silk. Then by proper easy fittings one end of one of these plates is connected with the primary current wire on one side of the breaker & the other plate with the same current wire at the other side of the breaker - hence the good effect.

Ever dear Gassiot Truly yours | M. Faraday

17 Jany 1854

Endorsement: Grove PM. Vol 4 501 | 4 series¹

Ruhmkorffs small coil

30 metres long

2 millime diameter

200 convolutions of the wire

2503 metres length

1/4 millim diameters

10,000 convolutions

Primary wire 2 1/2 mil. thick = .08 Inch

40 metres long about 1560 feet

300 turns

Secondary 1/3 mil. thick - .01 inch

70,000 metres 227,500 yds above 116 miles

30,000 turns

Millimetre = .03957 Inch

Metre = 39.37100 Kater² PT 1818 | 39.370079³