50 
ERICCSON’S PROPELLER. 
the subject demands. Our investigations have been hitherto exclusively confined 
to that of the Archimedes, not only because it is the successful trials with that 
vessel that have produced the interest and favourable impression now existing 
towards this kind of propeller, but because these are the only comparative experi 
ments, and therefore the only ones of real practical value. 
The satisfactory results have already produced an effect invariably attending 
success, namely, that of bringing forth a number of patents for modifications 
approaching the character of their progenitor. It would be impossible to notice all 
these within the limits assigned to us ; and we shall therefore proceed to describe 
such of them only as have been actually tried or are about to be introduced into 
practice. 
ericcson’s propeller. 
In the year 1838 Mr. Ericcson obtained a patent for a species of propeller of the 
form represented in the diagrams figs. 37 and 38. It consists of six blades 
Fig. 37- Fig. 38. 
aaaaaa, set at equal distances round a cylinder, which is concentric to the 
axis b. The blades and arms are segments of a screw. 
It appears that a vessel called the ‘ Robert Stockton ’ was tried on the Thames 
with a propeller of this description. Her power is stated to have been 60 horses, 
consisting of a pair of non-condensing engines placed at an angle of 90° to each 
other, and acting upon one crank, so that the motion of the screw axis was 
obtained at once from the engine. The cylinders were 16 inches diameter, and 
the length of stroke 18 inches; the pressure of the steam is stated to have been 
about 40 lbs. per square inch.