318 



In describing the construction and operation of the instrument, 

 he exhibited an enlarged drawing of the whole apparatus and its 

 several parts, together with specimens of the records as actually 

 made by it, and of the curves of mean temperature derived from 

 them, which had been furnished by the inventor. 



The part of the instrument forming the thermometer proper 

 consists of a cylindrical bundle of iron and brass wires (No. 13), 

 about 15 inches in length, so arranged as to be equivalent to 

 about forty-five inches of iron wire antagonized by about an 

 equal length of brass wire. The bundle is composed of five 

 pairs, two of brass and three of iron, arranged alternately around 

 the centre, and a single wire of brass, equivalent in action to a 

 third pair of that metal, placed in the axis of the cylinder. 



The upper end of the central wire, moved by the difference of 

 expansion of the two metals, operates upon the short arm of the 

 first of-a train of two levers, and through them upon the axle of a 

 pulley. To the grooved circumference of the larger wheel of 

 this pulley is attached a slender silk cord carrying the registering 

 'point designed to mark the temperature, and which, by the multi- 

 plying effect of the mechanism, is moved over a space three hun- 

 dred and twenty times as great as the differential expansion or 

 contraction of the wires. 



The registering point, properly balanced by an attached weight, 

 and guided, in its vertical movements by two slender parallel rods, 

 is made to record the temperature on a fillet of j)aper moved by 

 a train of cylinders whose axes are parallel to the guide wires. 

 The record is impressed by the impulse of a hammer striking 

 upon the back of the registering point at regulated intervals, and 

 thus producing a series of small perforations in the paper, the 

 hammer and the fillet of paper both receiving their motion from 

 a train of clock-work of peculiar construction connected with the 

 apparatus. 



The projecting shaft of the pulley carries an index, which, 

 revolving in front of a dial-plate placed over the pulley, enables 

 the observer to note the temperature as compared with the ordi- 

 nary thermometer, and to adjust the rod-thermometer to the stand- 

 ard whenever necessary. The adjustment is made by turning a 

 screw connected with the lower end of the central brass wire of 

 the thermometer. The latter instrument is on the outside of 



