60 REPORT — 1860. 



On an Atmotic Ship. By the Hon. W. Bland, New South Wales. 

 The proposal in this case was to employ a light keel and ship-formed body buoyed 

 up by an elongated balloon, and two heavy weights guided by a rope slung from 

 stem to stern, to alter the centre of gravity of the machine and direct its motion 

 upwards or downwards at pleasure. To cause it to move onwards in any assigned 

 direction, large but light and strong vanes were to be driven round, acting like the 

 screw propeller of a ship. 



On an Improved Instrument for describing Spirals, invented by Henry 

 Johnson. By the Itev. J. Booth, LL.D., F.R.S. 



Mr. Johnson's instrument, which, looking to its practical use, he calls a volutor, 

 admits of several varieties, and may be briefly described as follows: — The form 

 which most clearly exemplifies the principle consists of a vertical axis resting on a 

 horizontal plane, and retained on it by a metal point to prevent slipping or lateral 

 motion. To this upright axis is attached one extremity of the horizontal arm or 

 bar. The vertical axis passes through the extremity of the horizontal arm, or a block 

 attached to the end of it, in such a way that the horizontal arm may revolve freely 

 round the vertical axis. The remote extremity of the horizontal bar is furnished 

 •with a drum or pulley, over which a band or chain passes ; one end of this band is 

 affixed to the centre upon a level with the pulley, and the other end of the chain or 

 band, after passing over the pulley at the outer end of the horizontal rod, returns 

 and is attached to a slide which carries a pencil or marking instrument. The hori- 

 zontal bar is made to revolve, either by the hand directly applied to it, or by a string 

 wound round a drum attached to the block revolving on the vertical axis. 



The chain or band is thus wound round the upright axis, while each succeeding 

 coil encloses the preceding one, and is supported by a small plane projecting from 

 the centre. The slide is drawn from the centre towards the drum at the other end 

 of the horizontal arm, and thus the curve is traced by the pencil or other point, pro- 

 gressively increasing its radius vector as the slide recedes from the axis. The addi- 

 tion of small tubes to slide down, when required, to the junction, with an opening 

 for the chain or band, will afford the means of varying the size of the axis, and con- 

 sequently the interval between the successive spirals of the curve. The intervals 

 between the spirals are determined by the size of the axis, and the thickness of the 

 band coiled round it. When each coil round the cylindrical axis rises above the 

 preceding one, without enclosing it, the spiral of Archimedes is described, as the 

 radius vector is increased each revolution by the circumference of the axis, neglecting 

 the inclination of the cord. 



A cone may be conveniently used as a centre, and the band wound round it in lieu 

 of being wound in a flat coil ; and the size of the centre may be enlarged, by wind- 

 ing the band one or more times round the cone before tracing the curve. 



A number of pulleys are affixed to the slide and the block on the axis, and the 

 curve may be modified by passing the band over one or more of them. 



As the vertical axis of the volutor, and the slide on the horizontal bar to which 

 motion is communicated, are connected by a cord or chain passing over a system of 

 pulleys, the length of cord which wraps round the vertical cylinder becomes In times 

 the radius of the spiral, n being the number of pulleys attached to the slide which 

 travels on the horizontal arm. Hence, by increasing n, we may diminish the mag- 

 nitude of the spirals described by the volutor*. 



When, instead of the vertical cylinder round the axis, a grooved cone is sub- 

 stituted, the width of the whorls increases with each revolution of the radius vector 

 of the spiral ; and by substituting in succession a series of cones in the vertical axis, 

 each of a different pitch, we may obtain spirals where successive whorls shall widen 

 out in any given ratio. 



Recent improvements in the volutor, as shown in the annexed drawing, include 

 arrangements for the vertical position of the pencil, as also for attaching the band to 

 the base of the cone when required, and for applying the set of pulleys to either end 

 of the horizontal bar. 



* In fact, the cord wound round the axis, and the end of the slide which carries the 

 tracing point, are as power and weight in a system of mechanical pulleys. 



