a 
ON THE MEASUREMENT OF SHIPS FOR TONNAGE. 73 
are obtaining a preference over sailing vessels. On the contrary, it is essen- 
tial to fairness that such exemption should be given. Sailing ships already 
possess such exemption in the existing tonnage-law. The divisor 100, in 
the tonnage-law, gives that exemption. The real ton of freight is 40 cubic 
feet in most things, and, in some, 50 feet. The difference between the mer- 
cantile ton of 40 feet, and the imperial register ton of 100 feet, is designed 
to give the shipowner ample exemption for that portion of the internal room 
of a ship which is occupied by captain’s cabins, sailors’ berths, sails, cables, 
cordage, chains, anchors, sea-stores, provisions, and all the requisites of 
mooring and working the ship. This exemption has been recognized in all 
the tonnage-laws of this country. It has been merely extended to the steam- 
ship on the same footing—the propelling power, and all provisions for it, 
being included in a similar exemption. The error of the present law con- 
sists in making that exemption on an arbitrary tonnage, instead of the actual 
tonnage of engine room—an error which no time should be lost in re- 
medying. 
- 6. I do not see, and cannot imagine, why any exemption should be made 
other than that of the actual room occupied by engines, boilers, and fuel. 
7. The only true measure of power is the work actually performed by a 
marine engine; this work will vary-with the talent of the maker, with the 
care and intelligence of the keeper of the engine, with the age and condition 
of the boiler, and with the qualities and loading of the ship. In the absolute 
sense of true power, two engines, in which all the main dimensions are alike, 
and both perfectly new, will give out a totally different practical result. This 
_ is why the engine of one maker is well worth £60 per horse-power, and of 
another not worth £30. Yet, under varying circumstances, a given engine 
will perform double at one time from another. 
Owing, therefore, to the great variety in kinds and qualities of engines, it 
is neither politic nor expedient to attempt to define power in a form more 
absolute than the nature of the subject practically admits. The scale com- 
monly used among engineers for buying and selling engines is just as good as 
any other, so long as the talent of the builder and the knowledge of the uses 
is a main element of power of a marine engine. It is a question of name 
and character more than of dimensions and measure. Legislation cannot 
safely try to trammel such elements. 
8. Practically, Sterling’s rule, or Attwood’s rule, or Chapman’s rule, or 
any ordinary intelligent rule, will tell very accurately the cubic contents of 
-the inside of a ship. I do not see any grave fault in the present rule, though 
I will not assert that some more minutely precive rule for purposes of abstract 
science might not be given. 
Conelusion.—The result of considerable thought and pains given to this 
examination is that, in my opinion, we need not ask any alteration of the law 
regulating Imperial Register Tonnage, except the rectification of the allow- 
ance for engine-room, which remains fictitious and arbitrary. Neither should 
I recommend any further interference of Government officers with the regis- 
tration or working of ships or steam-vessels. I look for the advancement of 
naval architecture rather to the association of naval constructors and men of 
science with each other, and the mutual communication of their notions and 
knowledge, than to empirical efforts of legislation; and I hope for progress 
_ in navigation, rather from the general advancement of education and know- 
ledge, among all who are concerned in shipping, than from any trammels 
which, in the disguise of assistance and regulation, Government might be 
induced to impose on the captains and owners of ships. 
February 17, 1857. 
