MECHANICS AND USEFUL ARTS. 57 



shielding the ineffective surface of the propeller from the passing cur- 

 rent, and leading the water upon the fins at such a radial distance 

 from the axis as will secure the whole power applied in the right direc- 

 tion. By this alteration of the locality of the screw, the current is 

 thrown direct on the helm." 



IMPROVEMENTS IN THE CALKING OF VESSELS. 



In the construction of vessels the process of calking the seams so 

 as to exclude the water, forms an important part of the operation. 

 This has heretofore been done by chamfering the outer edges of the 

 planks, and then driving oakum or other similar material between 

 them. An objection to this mode of calking is the well-known fact 

 that the working and straining of the vessel has a tendency to throw 

 the oakum out, and render re-calking necessary, while, at the same 

 time, as the planks are not driven so close together, and consequently 

 cannot form a close joint, the hull will be less stiff and rigid than is 

 desirable. 



An improvement recently devised by Mr. B. F. Cook, of Boston, 

 consists in rendering the seams water-tight by placing between the edges 

 of the planks some adhesive elastic substance or material, such as 

 india rubber, gutta percha, or compound of both. This may be 

 done by forming a groove in the centre of the edge of each plank, and 

 placing in the said groove a strip of india rubber, gutta percha or 

 other elastic material, and then driving the planks closely together, 

 the edges of the planks not being bevelled but square, so that they 

 will form a close rigid joint. This strip of calking may be round and 

 tubular, or of any other required form, so as to fill the channel, which 

 may also be of any shape desired the planks thus grooved or 

 plowed are then driven together, with a coat of elastic cement be- 

 tween them if it is thought advisable. By the above method of calk- 

 ing a vessel, it will be seen that the necessity for chamfering the 

 edges of the plank is entirely obviated, and by cutting the edges 

 square, and placing between them an adhesive elastic substance, the 

 joint will be impervious to water, and at the same time the hull remain 

 extremely stiff and firm, while the calking cannot be worked out by 

 the straining or working of the vessel, as frequently occurs in the 

 method of calking heretofore practised. 



EXPERIMENTAL INVESTIGATIONS ON THE PRINCIPLES OF LOCO- 

 MOTIVE BOILERS. 



The following is an abstract of a paper recently read before the 

 Society of Civil Engineers, (England) by Mr. Clark of Edinburgh. 

 It commenced with some historical facts in locomotive progress, show- 

 ing that the general design of the locomotive was matured, imme- 

 diately after the trials on the Liverpool and Manchester Railway in 

 1829 combining the multitubular horizontal boiler, the horizontal 

 cylinders, and the blast pipe. Reference was made to the various 



