198 REPORT—1840. 
engines. Several experiments had been made at their request, and the 
following was the result :— 
Feet stroke. Lifted one foot. 
Wheal Vor, Borlase’s engine ......... 80 in. single 8°0 ......,.5.5. 123,300,593lbs. 
Fowey Consols, Austin’s ...........0+6 SO cane ispesee 9:0) gases ge apte 122,731,766 
Wheal Darlington engine ............ te DE PARES CUD sete 78,257,675 
Charlestown United Mines............ SO ys vaecoee ft pee ets 55,912,392 
Ditto Stamping engine ............... 32 ,, lifting 66 stamps... 60,525,000 
Wheal Vor, ditto .......:s.ssceceee eves 36dble. lifting 72 stamps... 50,085,000 
On the Application of Native Alloy for Compass Pivots. 
By Capt. E. J. Jounson, RN. 
Among those portions of a ship’s compass which most affect its work- 
ing, are the pivots and caps on which the needle and card traverse, and 
which, like the balance of a chronometer (but of far more importance 
to the practical navigator), should not only be fitted with the most 
scrupulous attention to accuracy, but be made of materials capable of 
maintaining a given form under the trials to which such instruments 
are necessarily exposed. Having examined a great variety of com- 
passes which had been used at sea, wherein Captain Johnson noticed 
that their pivots were generally injured, and often by rust, he searched 
numerous records of experiments for its prevention, and for improving 
the quality of steel in other respects, by means of alloys of platinum, 
coe a silver, &c. (he alluded particularly to the experiments of 
r. Faraday and Mr. Stoddart); and Mr. Pepys having obligingly 
supplied Captain Johnson with specimens of similar kinds of steel to 
those used by them, these examples, together with pivots made of the 
ordinary kind of steel, and hardened and tempered in the manner re- 
commended by eminent instrument makers, were placed in a frame for 
experiment; and to these again Captain Johnson added certain contri- 
vances of his own, such as rubbing a steel pivot with sal-ammoniac, 
then dipping it into zine in a state of fusion, and afterwards changing 
the extreme point. Some specimens he coated with a mixture of pow- 
dered zine, oil of tar, and turpentine; and others again were set in 
zinc pillars, having small zine caps, through which the extreme point 
of the pivot protruded after the manner of black-lead through pencil 
tubes. The whole of the specimens were then placed in a cellar, occa- 
sionally exposed to the open air, examined from time to time during 
more than half a year, and their several states, as respected oxidation, 
duly registered. Without going into the details of this register, the 
general result was, that not any of the kinds of steel pivots used in this 
trial, except such as were coated with zinc, remained free from rust, 
while the pivot made of the “ native alloy” which is found with plati- 
num, completely retained its brilliancy. Captain Johnson then applied 
a more severe test to this singular substance, first, by placing sulphuric 
acid, and then nitro-muriatic acid upon it; but even under this trial he 
could not observe that any change had been effected, although the 
blade of a penknife, subjected to a similar process, was rusted to the 
a 
