1818.] Mr.. Dick on a Spiral Oar. 439 



disagreeable associations, they are, perhaps, better forgotten. 

 There is, however, a fragment connected with this scheme, 

 which I think ought not to be lost, as it seems to promise to 

 be of great utility. The invention to which I allude is the 

 employment of a spiral oar ; and as Mr. Scott has kindly per- 

 mitted me to use every freedom with his communication, 1 shall 

 venture to offer it to you. I must however, confess, that my 

 limited knowledge of mechanics makes me hazard any remarks 

 as to the variety of its possible applications with very great 



diffidence. 

 The figure which accompanies this is not meant as an accu- 



rate fac simile of Mr. Scott's drawing, which is of proportions 

 somewhat different, being more particularly adapted to the 

 object he had in view ; it is rather intended to convey a notion 

 of the general principle of the spiral oar. It is extremely 

 simple in its construction . It may be made of any given diameter, 

 and the twists of the spiral fin twining around it, may be placed 

 nearer to one another, or more distant, and the fin itself may 

 be more or less expanded, as may be judged most expedient, 

 and the materials also may be suited to the particidar purpose 

 the mechanic may have in contemplation. 



When it is to be applied, as Mr. Scott intended, to each side 

 of a ship, or boat, for propelling it through the water, he 

 says, it must be made of a size every way corresponding to that 

 of the body it is required to move. In this case there should 

 be a strong iron axis, somewhat longer than the proposed 

 length of the oar ; in this, a hollow cylinder of plate copper, 

 made water-tight, should be fixed, in which the spiral fin 

 (made of the same material) may be inserted, running like 

 a screw around it, as represented in the figure. The dia- 

 meter of the cylinder must of course be proportioned to that 

 of the projection of the fins; and I may remark, that the 

 proportion of the latter, in the figure, would probably be 

 found to be too great, compared to that of the former, if the 

 oar were to be constructed for the purposes of navigation. The 

 greater the diameter of the whole oar, and the greater the 

 distance between each twist of the spiral fin, the greater will be 

 the resistance it will meet with in revolving under water, and the 



greater will be the effect produced in accelerating the progressive 



motion of the vessel. 



It is unnecessary for me to state Mr. Scott's methods of 



appending these spiral oars, or of giving motion to them ; were 



I to describe these, several plates would be necessary ; and I 



