396 Progress in Science. [July, 



current, the exterior tube the induction tube, and the interior tube the 

 projector. Substitute for the exterior tube filled with air a gas main of 

 the proper diameter filled with gas, communicating through the outlet with 

 the gasholder, and through the inlet with the retorts ; substitute for the cen- 

 tral jet of breath a jet of high pressure steam, and you have at once a working 

 gas exhauster complete in all its essentials. In practice, a projector with 

 orifice f inch diameter, and a cylindrical induction pipe 3 feet long and 

 4 inches diameter, have been found sufficient to pass 50,000 cubic feet of gas 

 per hour against a back pressure equal to 13 inches of water, and to maintain 

 a steady vacuum of 2 inches in the hydraulic main. 



Mechanical Engineering — Testing Rails. — The importance of instituting an 

 efficient test for rails has been brought before the notice of the Institution of 

 Civil Engineers by Mr. James Price. There are certain causes of increased 

 wear in rails which can be avoided ; first, the difference in the forms of rail- 

 tops on lines worked as one system, the tyres which run on one portion not 

 fitting the form of rail-top on other parts ; and, secondly, the super-elevation 

 of the outer rail on curves not being properly attended to. To facilitate cal- 

 culation in the latter case, the author had invented a rule which left out the 

 term radius — a chord being found, the versed sine of which was the correct 

 super-elevation for any curve. This chord, for a speed of 40 miles per hour, 

 was 64 feet for the English gauge, and 67 feet for the Irish gauge, a chain 

 length (66 feet) being sufficiently near for either. For any speed and any 

 gauge the rule was — " Length of chord whos e versed sine equalled super- 

 elevation = J velocity in feet per second X 1 / gauge." 



The qualities sought in a rail are fourfold : — 1. Strength as a girder, to sus- 

 tain a moving load ; 2. Toughness, to resist sudden strain or impact ; 3. Soli- 

 dity to resist separation under pressure ; and, 4. Hardness, to resist wear of the 

 surface. The flange, or Vignoles rail, stands first as to form, for strength, and 

 the double-headed rail comes next, while the bridge rail is a bad girder form, 

 and 30 per cent of such rails break before they are worn out. 



Existing modes of testing rails may be divided into — 1. Dead weight test, 

 which is valueless as not being analogous to actual work ; 2. Falling weight 

 test, which is unfair, serviceable rails being rejected by it, as it goes as far 

 beyond the requirements of practice as the former test falls short of it; 3. The 

 examination of fracture to ascertain structure is a matter of too great nicety 

 for general use. The machine used by the author for testing rails subjects 

 them to wear analagous to actual use. It consists of a pair of metal rollers, 

 5 feet in diameter, 16 inches wide, and weighing 2j tons each, supporting a 

 circular frame or beam weighing 6J tons ; this frame being connected by radii 

 with a centre boss, through which passes a vertical axis. The circle traversed 

 is 40 feet in diameter, and the pressure borne by the rollers is 6 tons and 5 tons 

 respectively. Motion is communicated by a steam-engine, and the machine 

 can be worked at about 20 miles per hour ; but it is generally run at a speed 

 of about 13 or 14 miles per hour. The rollers are caused to revolve over a 

 ring or polygon of the rails to be tested until they are broken or worn out, and 

 they bear with a weight equal to that of the driving wheel of a locomotive. 



Sea Waves. — At the Friday evening meeting of the Royal Institution of 

 Great Britain, May 26, 1871, Dr. W. J. Macquorn Rankine, C.E., F.R.S., 

 delivered a most interesting lecture on this subject. In the first place he gave 

 a summary, illustrated by diagrams and machines, of existing knowledge of 

 the mode of motion of water in waves, and of the geometrical and dynamical 

 laws which govern the relations between the depth of disturbance of the 

 water, the velocity of advance of waves, their periodic time, and their length. 

 He referred to the experimental and theoretical researches of previous 

 authors on the subject, such as the Webers, Airy, Scott Russell, Caligny, &c. 

 He then explained the principle, of which Mr. Froude was the first to 

 point out the importance, that the action of water agitated by waves upon a 

 ship tends to make her perform the motions which would have been performed 

 in her absence by the mass of water that she displaces. In still water, 



