32 REPORT—1852. 
The author then traced the consequences of such combined motions, by supposing the 
disturbance to commence first around one of the poles of the earth, and then by 
tracing the change of circumstances which must take place in other latitudes; and 
asserted, that by calculating by these suppositions, using as data the well-ascertained 
dimensions of the area over which cyclones extended, a relative movement of the air 
over the earth, even greater than any that had ever been observed in violent hurri- 
canes, might result. He concluded by showing how an experiment which he had 
prepared might be performed, so as to exhibit the more striking effects of a hurricane 
in water, by giving a whirling motion to a wide vessel of water furnished with a 
valve in the bottom, at a distance from the axis, which could be withdrawn. He 
also stated his conviction, that the phenomena of sea and land breezes would yet be 
found to partake of the rotatory character. 
Aurora Borealis observed at St. Ives, Hunts. By J. K Warts. 
This is a record of four displays of the aurora on the 26th of March, 1851, and on 
the 19th and 21st of February, and the 21st of March, 1852. 
MIscELLANEOUS. 
On an Instrument for Drawing. By Henry TwInine. 
The use of the instrument is to assist in obtaining correct representations of ob- 
jects from nature, by pointing out the different angles at which they present them- 
selves to the eye, and by finding out the vanishing points of their retiring sides. 
The instrument consists of a graduated semicircular plate placed horizontally 
on the top of a rod or pillar, so as to be raised or lowered at pleasure. Above 
this plate or dial is placed another having a vertical position, in connexion with 
which there is an index or needle, moving vertically on a pivot, and which 
serves to mark the elevation and the depression of any point above or below the 
horizon. Also connected with the horizontal plate or dial is another index, con- 
sisting of three branches or wires placed at right angles, and which is susceptible of 
a horizontal motion. Its position is immediately above the horizontal graduated 
plate. The straight side of this plate is placed parallel with the picture, the angular 
dimensions of which are marked on the graduated semicircle opposite. The cross 
wire of the index above the plate is then so directed, that, to the observer’s eye, it 
will correspond exactly with a given line of any object in nature of which it is 
wished to obtain the direction, or, in other words, the inclination with reference to 
the plane of the picture. A plan recommended by Varley for attaining this purpose, 
is to give to one of the limbs of a jointed rule the inclination which any receding 
line in nature may appear to have to the eye; but with the instrument now described 
we reverse the method, as it were, for we adjust the direction of a wire which is 
level, so as to correspond with the horizontal line of any retiring object, and then we 
find out, on the graduated plate connected with the wire, the exact position of the 
vanishing points of these objects, that is to say, those points to which their various 
horizontal lines converge. Thus the true inclination of all horizontal lines is 
obtained by finding out, in the first place according to a simple method, but which 
cannot here be fully detailed, the vanishing points of all level lines of objects. 
The advantages of this instrument may be considered to consist in accustoming 
the student to view the perspective of objects theoretically, and in a manner calcu- 
lated to impress its principles on the mind; the horizontal plate and index serving 
to convey clear and precise notions of the relations of the vertical surfaces of objects 
to the plane of the canvas, whilst the vertical plate and needle serve to give the 
angular elevation and depression of objects, or their extension above or below the 
horizon ; a correct representation of nature, under various circumstances, requiring 
a perfect familiarity with both these principles. 


