10 Transactions.— Miscellaneous. 
Авт. II.—On Observed Irregularities in the Action of the Compass in Iron 
Steam Vessels. By A. H. Ross. 
[Read before the Otago Institute, 11th November, 1873.] 
Ir would be extremely difficult to say how many or how few of the casualties 
which have occurred on the New Zealand coast to iron-built steamers, which 
have been engaged in its navigation, may be attributed to compass errors. 
I have little doubt, however, that a great proportion of them are attributable 
to that cause, and I have less doubt that, if so, the cause is preventable. 
How? let us consider. As I intend this paper to be of an entirely practical 
character, I shall not introduce into it any of the investigations of the subject 
which have been made by Professor Airy and other eminent men, with a view 
to discover such general laws of the magnetic disturbance in iron ships as 
enable us to correct the local attraction. I will simply enumerate a few 
observations of the action of compasses on board two of our coasting 
steamers, taken by myself during the present year, and offer a few remarks 
with a view to the removal of what I consider to be a source of great danger 
to life and property, viz, the navigating of our iron-built screw steamers by 
means of tabulated cards of deviations. 
On the deck of one of the vessels on board of which I took notes, two 
binnacles were placed, in each of which was suspended an apparently well- 
made compass ; one was placed immediately in front of the wheel, the other 
about thirty feet forward. Upon no course steered during the voyage did the 
compasses indicate alike ; there were continual, though not constant, differences, 
varying with every change in the direction of the ship’s head. The least 
difference which I observed amounted to about 12 degrees—a little over one 
point : this occurred when the vessel's head was N.N.E. ; the greatest, about 
27°, or nearly 24 points, when the direction steered was W.N.W. These 
notes were taken when making the northward voyage. The southward voyage 
I made in another vessel; the compasses on board were placed somewhat 
similarly to those in the first ship, the distance between them being, however, 
not quite so great. The difference between the indications of the compasses 
were much greater than in the former case. I noted them carefully, as 
follows :— 
lst. Stern compass, W. 3 8. 
Forward bue S.S.W.18. 
2nd. Stern compass 
Forward rua SS.W. 
j Difference, 78° 45’, or 7 points. 
| Difference, 67° 30’, or 6 points, 
3rd. Stern compass, W.N.W. i | ; : 
Forward compass, S. W. j W. | Difference, 61° 52], or 5} points. 
