10 Transactions. — Miscellaneous. 



Art. 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, 1S73.] 

 It "would be extremely difl&cult 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 1 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 tlie 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 boai^d of which I took notes, two 

 binnacles were placed, in each of which was suspended an apparently well- 

 made compass j 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 2 J 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 .• — 



1st. Stern compass, W. 4 S. ) -ps-iir ^-oo .-/ -. . 



-ri 1 aoiwT 1 c! > Dinerence, ^8 4o' or t points, 



tor ward compass, S.S. W . ;| S. j ' ' '^ 



2nd. Stern compass, W. ) n-a- n"o or\r n 



TTi 1 a a ATT ^ Dmerence, b / dU , or 6 points. 



Forward compass, S.S. W . J ' ' i '^• 



3rd. Stern compass, W.N.W. \ t^-cc r^oc;n^, ei • , 



TP 1 c ATcr 1 -nT > Dinerence, 61 52i , or 5i points. 



Forward compass, fe. W . | W. J ' -^ ' 2 i" "''^' 



