ON GBAPEIC METHODS IN MECHANICAL SCIENCE. 393 



ings reduced to any datum level being obtained direct, and witbout any 

 calculation. And it enables tbe operations of taking soundings and plot- 

 ting the same to be performed simultaneously and by one person. 



The apparatus consists of a sounding-machine, a distance-recorder, 

 and a section-plotter. The sounding-machine consists of a wheel with a 

 spiral reel attachment ; around its periphery is wound a wire by which a 

 lead is suspended, and the spiral reel carries a preventer line, one end of 

 which passes through a leading-block fixed at the forward end of the 

 boat on which the apparatus is mounted, and thence it is taken back to 

 the lead, to which it also is attached. A wheel and reel are employed so 

 proportioned relatively to each other and to the base that they both pay 

 out or take in the required amount of their respective lines to maintain 

 the lead vertically under the after-end of the base line at all depths of its 

 range. The wheel is 10 feet in circumference, and its rim is divided into 

 feet and tenths of a foot. One end of its axle has a sleeve-bearing, to 

 which are attached a long pointer and a short one, the longer pointer to 

 indicate readings on the rim of the wheel, and the shorter one to show the 

 reading on a fixed disc which is marked similarly to the wheel. 



The section-plotter consists of a paper feed-roll, actuated so that the 

 travel of the paper represents to the required scale the paying out of the 

 distance wire. A block, sliding in guides, carries a marker across the 

 paper at right angles to the line of its travel ; it is actuated by a cord 

 from a small barrel clamped to one end of tbe axle of the sounding-wheel, 

 capable of being turned about the same for adjustment, and so propor- 

 tioned as to indicate, on the required scale, the rise and fall of the lead 

 by the motion it imparts to the marker. 



The plotting of the soundings is effected by simply tapping the marker 

 — which is kept clear of the paper by a spring — each time the lead is felt to 

 touch the bottom, and thus there is produced a dotted section to a trial 

 datum, from which, and from a tide-gauge record, the true datum line 

 may be plotted, time having been noted at each end of the line. The 

 position of cross-sights, bearings, &c., may be indicated by holding the 

 marker in contact with the paper while the lead is being raised, so as to 

 produce a vertical stroke, the particular mark so obtained being desig- 

 nated by a note written against it. 



Mr. F. G. Baily, B.A., A.Inst.B.E., has kindly furnished the follow- 

 ing notes on the plotting of curves for practical electrical work : — 



' In the science of electricity and in the practice of electrical engineer- 

 ing the employment of graphic methods is very general. The curves 

 may be used as the numerical interpretation of calculated formulas, or as 

 a means of giving in a connected form the results of a number of experi- 

 mental data which frequently are not amenable to mathematical treat- 

 ment, and cannot be embodied in algebraic form. 



' One of the earliest and simplest examples of the latter use is the repre- 

 sentation of the magnetic field of an electro-magnet or permanent magnet 

 by Faraday's lines of force, and the method has been greatly developed 

 of late years in the researches on powerful magnets, and in dynamo- 

 electric machinery. 



' In connection with this a very important curve of the magnetic 

 properties of metals has formed the subject of much work, carried out 

 principally by Rowland,^ J. Hopkinson,^ and Ewing,^ and the results 



• Phil. Trans., May 1873. » Ihid., 1885. 



