360 On the best Kind of Steel and Form | 
the directive force, the compasses on board had become nearly 
useless. Some of the azimuth compasses employed on that oc- 
casion were of my own invention; I was therefore anxious that 
the next expedition, which was about to sail under the command 
of Lieut. Parry, and which has happily returned with so much 
honour to those engaged in it, should be furnished with instru- 
ments of this description, combining as much power and sensibi- 
lity as possible. 
It was with this intention alone that I commenced the expe- 
riments which form the subject of the present paper ; but which 
I should -not have deemed sufficiently important to be made 
public, had I not lately, on resuming the inquiry, been led to 
some results which appeared of sufficient interest, as well as prac- 
tical utility, to induce me to lay them before the Royal Society. 
My immediate object was to ascertain the kind of steel and 
form of needle best calculated to receive the greatest directive 
energy with the least weight. 
Two needles were prepared of that kind of steel which is called 
hlister-steel, and two of spur-steel, the weight of each being 
sixty-six grains. They were of the form of a long ellipse, in 
length five inches, and in width halfan inch. One of each kind 
was pierced, as in the figure below, the weight being made up 
by additional thickness, This needle, therefore, had much less 
extent of surface than the solid ellipse. 
Recollecting to have had in my possession, many years since, 
a compass of extraordinary power, the needle of which was com- 
posed of pieces of steel-wire put together in the shape of a 
rhombus, I caused two needles to be made of this form of a piece 
of clock-spring, which I understand is of that kind of steel which 
is called shear-steel. They were shaped as below; in one, the cross 
piece was of brass, and in the other formed of part of the clock- 
spring. These needles were, by mistake, made to weigh only 
45 grains, 
In ascertaining the directive force, the balance of torsion of 
M. Coulomb 
Pe. 
