work, the remainder being devoted to hydrostatics of ship construction, tonnage measurement, stability, the action of sails, resistance of vessels and other scientific matters relating to naval architecture. This part, while treated with great thoroughness, is yet simpler than most works on this subject, being almost entirely free from higher mathematics, a consideration of importance to those, who, after years of practice in the engineering profession, have become somewhat rusty in the integral and differential calculus. J. H.
THE ASHCROFT .~ANUFACTUKIN(; CO.1IPAx1”S IMIWOVED TABOR INDICA- TOR. In this improvedinstrument, the arrangement of the parallel motion mech- anism is reversed, by which means a range of motion of the pencil of 3.25 inches is obtained. The curved slot by which the pencil is made to move in a str:$$t line is transferred from the piston rod to a stationary guide, firmly secured to the cover of the cylinder. In the new instrument the roller is the moving part, whereas in the old instrument it was stationary. By the above changes the parallel motion multiplies the piston movement five times. The treatise accompanying the instrument is designed for reference and contains instructions for purchasers and others interested in the subject. Mr. Barrus’ directions respecting the manner in which the improved instrument should be used are exceedingly clear and concise, and are of a thoroughly practical character, giving full instructions as to the best methods of securing the instrument, giving motion to the paper, etc., and, in fact, in- cluding everything which it is necessary to say upon the subject. LE VAN.
SCIENTIFIC NOTES AI\TDCOMMENTS. .-- TECHNOLOGY. , Ttm ZEUNER VALVE DIAGRAM. John L. Gow, Assistant Engineer, IJ. S. N.---In the application of the %euner diagram to valves fitted with link motions giving unequal leads for different positions of the link, the use of the graphical method of solution becomes more complicated from the fact that the centre of the valve circle moves in the arc of a parabola as the link is raised or lowered. That is, in the figure if C, C,, C,, are the centres of valve circles corresponding to three different positions of a Stephenson’s link, then the curve C C; CLis a parabola, A circle whose centre is on the line XX, and passing through the points L’ and C<,will be found to practically coincide with the part of the parabola used in the diagram. To draw this circle the following method is given, In the figure suppose L‘ to be the centre of the valve circle when the link is in full throw. From C draw the line C B at right angles to 0 X1, and make C B equal to the length of the eccentric rod. At R draw a line parallel to 0 X1, and lay off a distance B D equal to the half length of the link, to the right if the rods are open and to the left if crossed. Join L‘and D and the point CAwhere C’ n crosses 0 X,, is a second point in the /_.______~. I i? /I
0 Xl, and take the point C’,where it cuts the circle as the centre of the vaive circle and C; 0 as a radius. If 0 I/is the steam lap and 0 Vthe exhaust lap, the steam port opens when the crank gets to 0 I’;, and closes at 0 7; and the exhaust port opens at 0 I/,, and closes at 0 14. The travel of the valve as given by Zeuner, third edition, p. 63, for Stephenson’s link with open rods, omitting the last term is
in which 7. is the half travel of the valve, rYis the angle of advance, c the half length of the link, u the distance the link has moved from its central point, I the length of the eccentric rod, and IJ is the amount the crank has moved from the dead point. For different positions of the link, or different values The point (‘is usu:~Ily determineti ;r;~ phically in using the diagram. If // = 0 or the link :6 in mid-position ?heli the co-ordinates become
‘1‘0 prove that our construction makes
and from the figure
and
as before. As we have never seen an easy method by which the influenceof the link could be graphically laid down, it is believed that the method above given will allow the entire distribution of steam to be investigated without any other work than can be done on a drawing board. H. W. S ESGINI.:S. John 1.. Cow, ..\ssistant Engineer, U. S. S.-Assume that Kg, I represents the combined theoretical cards for an engine having z cylinders. I.et ri, be the volume of the high pressure cylinder to the point of cut-off;
I/, , the total volume of the first cylinder; P, , that of the second; . . . V, , that of the last or low pressure cylinder. Let P, be the initial absolute pressure and <, the final back pressure. Assume that the law of the expansion is P V = a constant, and that the expansion in the rzth cylinder is carried on to the back pressure line, If Y is the total number of expansions then D Y = ;,’ .
” The area of the entire card will then be
.a2 = P, v, (I -c Q Below the line II n the area of the card is and below any line as the rtth the area is and combining (I) and (2) we have 259 or, as P, 1: = P, VI , iy, = n-d ...... (3) Y * To apply this formula to a triple expansion engine n = 3, and making d = I and 2, we have for the horse-power cylinder and for the intermediate cylinder For a quadruple expansion engine the cylinders would be Equation (3) can be put into a more convenient form by putting YD”L for V 4 D being the diameter of the cylinder and L the stroke. The formula then becomes or the diameter of any cylinder can be formed directly from the ratio of expansion and the diameter of the low pressure cylinder. An application of this formula to many of the triple and quadruple expansion engines lately built will show that the dimensions obtained from the form&e agree very well with recent practice. The following are some of the latest quadruple engines built : Carcuzated. H. P. L. P. Second. Third. Smand. T&d County of York, . . . . 20 57 ZS’A -40 28’34 40.2 Grace Darling, . . . IO 28 ‘4 20 14’9 lg.86 Myrth, . , . . . . 12 34 ‘7 24 16.98 24-X City of Venice, . 30 70 40 52 39‘78 52’77 Buenos Ayres, . . 32 92 46% 64% 45’50 64’80 Suez,...... 22 62 10 43 31’1’ 43’89 H. W. S. .