ON GRAPHIC METHODS IN MECHANICAL SCIENCE. 40{> 



By having a straight-line motion instead of employing the arc of a 

 circle, the above kind of ruled paper is not a necessity, and the area of 

 the curve, when desired, is more easily obtained. With the larger instru- 

 ments, such as those of Mr. Bailey, a small chariot is often employed for 

 carrying the pencil, and this runs to and fro on rails above the drum, 

 which is placed horizontally. The chariot itself is loaded, and the pencil, 

 as already mentioned, is also loaded, but with much smaller weights. 

 Figs. 32, 33, and 34 show the kind of chariot which has been largely 

 used in the case of tide-gauges and reservoir-level recorders by Mr. 

 Bailey. 



It may be mentioned generally that it has become the custom to 

 ahvays encase such recording instruments ; usually a glass front is em- 

 ployed, so that the kind of record being taken can be seen on inspection. 

 Mr. Bailey has found, after much experience, that it is better to use cast 

 iron for the case, as the change of form of wooden cases often led to 

 errors in the instrument. 



3. The means by which the position of the recording point is regu- 

 lated may be made the basis of classification for self-recording instru- 

 ments, as follows : — 



a. Level of water, mercury, or spirit. 

 h. Pressure of steam, air, or water. 



c. Magnetic attractions for electrical purposes. 



d. Velocity. 



e. Temperature. 



/. Vibrations and shocks. 



g. Change of position from loss or gain of weight. 



h. Chronographs, tell-tales, and similar instruments. 



These headings will now be taken seriatim. 



a. This class includes various kinds of tide-gauges, reservoir and 

 boiler level recorders, recorders for the depths of wells or record of rain- 

 fall, and for the height of the barometer. 



A large instrument of this kind, which also records velocity, made by 

 Messrs. Bailey, has been described in a paper by Mr. Hurtzig ' as follows : 



■ A ball-float moving in a tube actuates a pencil, which records, on a 

 sheet of paper upon a drum revolving by clockwork, the varying heights 

 of the water, 2 inches on the diagram being equal to a fluctuation of 

 12 inches of water ; the diagram revolves once in twenty-four hours — 1 

 inch=l hour. For recording the velocity it was determined to register the 

 angular displacements of a spherical ball which, when at rest, was 

 suspended in a vertical position, with its centre coinciding with the centre 

 of the 5-foot culvert. This ball is attached to the long arm of a lever 

 pivoted to a small bracket fixed to the top of the culvert. 



'The short arm of the lever is connected by a platinum wire and 

 system of levers, all duly counterbalanced, with a second recording- 

 pencil upon the revolving drum. 



' The recording diagram indicates the level and velocity for a period of 

 twenty-four hours. That portion of the diagi-am referring to level is divided 

 so as to give actual depths of water upon the sill of the sluice, the conditions 

 of the clause requiring that when the depth reaches 4 feet 6 inches, and 

 the sluice doors are closed, pumping must be carried on. 



' ' Tide-gauge Eecorders,' by A. C. Hurtzig, read at the International Congress of 

 Inland Navigation. 



