ON AN IRON STEAM-VESSEL. 
287 
attraction of the vessel, the object of some of the experiments above enumerated (and 
which suggested themselves to me during the course of my inquiry) is to determine 
whether the causes that affect the direction of the magnetic needle on board an iron 
steam-vessel are constant or variable ; and whether, should they prove to be the 
latter, that variation may amount to such a quantity as would be seriously detri- 
mental in a practical point of view ; or to prove that under ordinary circumstances 
the directive power will be sufficient for all the purposes required. 
Some striking facts respecting the local attraction of ordinary steam-vessels having 
come under my immediate notice, I have considered it my duty to detail them at the 
end of the report of experiments, and have added some practical observations on 
placing compasses on board steam-vessels generally, to which I beg you will call Their 
Lordships’ attention. 
Hoping that the results which have been already obtained will not only be advan- 
tageous as a guide to future experiments, but also that they will prove useful in the 
practice of navigation, I have now to request that you will be pleased to lay this 
Report, with the accompanying Tables, before my Lords Commissioners of the 
Admiralty. 
I have the honour to be, Sir, 
Your very humble Servant, 
E. J. JOHNSON, 
Commander R.N. 
To Charles Wood , Esq. M.P., 
Secretary to the Admiralty , 8$c. 8$c. 8$c. 
Table 
