BLAXLAND’S PROPELLER. 
59 
equidistant from the main axis. The ends g of the rods e are screwed and fitted 
with nuts, so that by screwing up those nuts the tightening drum can be drawn 
towards g, and tighten the ropes. 
Whatever tends to elucidate a mechanical discovery, especially in its infancy, 
is valuable to the community, and the experimentalist is entitled to our thanks 
even when he fails in his attempts. Failures, indeed, are the most useful part 
of our experience, on the same principle that we can only ascertain the strength 
of a body by its fracture. We have, therefore, described Mr. Blaxland’s pro 
peller, although it must necessarily be inferior in effect to the screw of the 
Archimedes: in the first place, because by his method of construction, the arms 
to which the blades are attached oppose their projecting surfaces to the water, 
and considerably increase the direct resistance: and, secondly, because the blades 
(being planes) are unequal in their effect; producing a much greater diagonal 
action on the water, except at one point, than if the same were formed as sections 
of a screw. On comparing Mr. Blaxland’s propeller with the screw, it is evident 
the former must be weaker and more liable to injury from the blades having no 
other support than that of the arms to which they are attached. In fact, there 
appears no obvious reason for the form here adopted, which seems to resolve 
itself into a method of making the screw by substituting circular blades for the 
triangular plates described and shown at page 15, as the mode of constructing 
the screw of the Archimedes. If this be the object, it is clearly inferior to 
the arrangement there adopted. 
The performances of the Swiftsure confirm the opinion we have expressed. 
It is reported that she increased in speed over her former rate about a mile and 
a-half per hour. Such extravagant statements invariably defeat themselves, and it 
may be asserted without fear of contradiction, that such an accession of speed with 
the same vessel and engines is impossible. The loss of power by the paddle wheel 
at ordinary immersions we have shown not to be greater than ^ths, and the 
increase of speed requiring an increase of power being as the square of the 
velocity, if the whole of the power could be applied without loss, like the teeth of 
a wheel acting in those of a rack, the speed would then only be increased |-ths 
of a mile per hour. If therefore the Swiftsure ever attained, as is asserted, the 
speed of nine miles per hour, there must have been some other alteration which is 
not stated; and if so, the whole experiment becomes valueless. If, moreover, this 
speed was attained, we find it has not been uniformly kept up, for on one 
occasion we learn the Swiftsure was beaten by the Novelty, a vessel of 320 tons 
burden, bark rigged, drawing between 9 and 10 feet of water, and propelled by 
two engines of about 12-horse power each, by a screw similar to that of the 
Archimedes, and having 150 tons of ballast on board. The Novelty passed the