52 ANNUAL OF SCIENTIFIC DISCOVERY. 



the two cylinders of a double engine in such a manner that their base or bot- 

 tom ranges with a plane passing through the axis of the propeller shaft, or 

 nearly so, in combination with a certain arrangement of rock-shafts, crank- 

 pins, and connecting-rods, for imparting motion from the pistons to the shaft, 

 whereby the inventor is enabled, firstly, to bring the cylinders nearer to the 

 propeller shaft, and hence to economize space, and construct the frame of the 

 engine of great strength and compactness. Secondly, to avoid the diagonal 

 thrust and friction of the slides, unavoidable when the connecting-rod is 

 attached directly to the cross-head. Thirdly, to operate the two connecting- 

 rods nearly at right angles to each other, which enables the inventor to pro- 

 duce a continuous motion with a single crank on the propeller shaft and a 

 single crank-pin in common. Fourthly, to employ a crank on the propeller 

 shaft much longer than half the length of the stroke of the piston, thereby 

 diminishing the heavy pressure on crank-pins and journals which has here- 

 tofore caused so much trouble by the overheating of the bearings, and at the 

 same time diminishing the strain on the engine frame. Scientific American. 



HYDROSTATIC SCREW-PROPELLER. 



The Southampton (Eng.) Star, daily paper, describes the successful work- 

 ing of a hydrostatic screw-propeller, or steamer driven without a shaft, and 

 says : " All that would be required for the largest ship afloat (by the adop- 

 tion of this invention) would be one horizontal steam cylinder, placed close 

 to the bottom of the vessel, connected to one pump, also laid on the bottom 

 of the vessel, close to the kelson, working fore and aft the ship without shaft 

 or crank ; and by forcing water through the hollow screw-propeller, produc- 

 ing a powerful rotary motion, where only it is required, namely, in the screw, 

 which can by this invention be driven continuously five hundred or more 

 revolutions per minute; and as the whole is immersed in a constant stream 

 of cold water, there is no possible chance of heated bearings. The water 

 surrounding it on all sides becomes a constant lubricator. The pOAver of 

 manoeuvring the propeller from the deck, no matter at what rate the vessel 

 may be sailing, is another peculiarity. 



ON BOILER INCRUSTATIONS. 



A series of papers on boiler incrustations have recently been published in 

 the London Engineer, by Mr. James Napier, a practical chemist of Glasgow. 

 The following is his analysis of scale taken from a boiler in which river 

 water had been used : 



Carbonate of lime 79.0 



Sulphate of lime 6.3 



Peroxyd of iron 35 



Silica 2.2 



Carbonaceous matter 4.0 



Water , 5.0 



100. 



The next analysis is that of scale taken from the boiler of a steamer run- 

 ning between Glasgow and Liverpool, in which no attention was paid to 

 "blowing off." The scale was composed of two layers; the one (that next 

 the metal) was hard and crystalline, the other (or outer coat) was softer and 



