306 STAFF COMMANDER EVANS AND MR. A. SMITH ON THE MAGNETIC 
We will now pause to state what is known of the value of * for iron of different kinds. 
The coefficient * is the quantity so designated by Neumann in Crelle’s Journal, 
vol. xxxvii. p. 21, Weber in Gotting. Trans, vol. vi. p. 20, and Thalen in Nov. Act. 
Soc. Reg. Upsal. 1861. 
It is related to the Tc of Poisson’s papers in the fifth volume of the ‘ Memoires de 
l’lnstitut,’ and to the g of Green’s celebrated “ Essay on the Mathematical Theories 
of Electricity and Magnetism ” (Nottingham, 1828 ; reprinted in Crelle’s Journal, 
vol. xlvii.), by the equation 
47 r 
— X 
Green, in the essay referred to, finds, from some experiments of Coulomb on steel wire, 
^=•986636, 
whence 
*=17-625. 
Weber finds the following values of * : 
Steel tempered to glass hardness and already magnetized . . . 4-091 
Steel tempered to glass hardness with no permanent magnetism . 4-934 
Soft steel 5-61 
Soft iron 36 
Thalen finds, from six specimens of soft iron carefully annealed, the following 
values : 
Specimen. x. 
1 34-58 
2 
3 
27-24 
45-26 
4 32-25 
5 44-23 
6 36-96 
Mean . . . 36- 75 
From observations of iron bars given by Scoresby in his 6 Magnetical Investigations,’ 
vol. ii. p. 320, we derive 
X. 
Iron rod, not struck 16-77 
Iron rod, struck .... ... 44*07 
From observations which we have made with a rod of iron x^-ths of an inch in dia- 
meter, 3 feet long, we have found 
X. 
Iron, not struck . 1^-48 
Iron, struck several sharp blows, about 80 
Hence probably in the iron plates used in ship-building * may vary from 10 to 30. 
