METEOROLOGY. 415 



in the rotation of the shaft, and is covered with a tin funnel to shed 

 the rain. The shaft and the vane are fastened together, so that the 

 former turns with the latter. The arrow part of the vane is formed of 

 a rod of round iron three fourths of an inch in diameter, and balanced 

 by a bob of lead. The feather part of the vane is composed of two pieces 

 of pine board about one foot wide, eleven feet long, and half an inch 

 thick. To give the instrument more sensibility in regard to the 

 changes of the direction of the wind, the feather part is bifurcated, as 

 shown in the section e. 



The lower part of the shaft, which is terminated in a hollow rectan- 

 gular box, carries a wooden clock on one of its vertical faces, as shown 

 in Fig. Gf. The whole weight of the shaft and vane is supported on 

 a pivot which rests in a hollow in the upper surface of a small iron 

 disc placed on the middle of the large sheet of recording paper, which 

 in turn, rests on the flat surface of a stout wooden table. 



The pencil, as shown at g, is supported vertically by two brass tubes 

 which slide, with some degree of friction, on two parallel rods of pol- 

 ished steel wire, projecting horizontally from the shaft, and is drawn 

 inward from the circumference of the paper towards its center by a 

 cord moved by the clock. The hollow part of the shaft which carries 

 the clock and the pencil is shown in section in Fig. h i. The cord is 

 fastened at one end to the pencil, then passes under a pulley or fric- 

 tion roller, to change its direction, and again is wound around another 

 pulley fastened on the projecting arbor of the main spring of the clock. 

 To keep the cord tight, and to assist the clock in moving the pencil, a 

 weight is attached to the other extremity of the cord. To prevent 

 this weight from coming in contact with the cord, the two are sep- 

 arated by a thin partition, shown in the figure. The weight is of 

 lead, of about five inches long, two and a half inches wide, and one 

 inch thick. 



The direction of the wind at a given time is recorded by the posi- 

 tion of the mark of the pencil on the paper. To ascertain the hour of 

 any change in the direction of the wind, the time at which the paper 

 is put on, and the time at which it is taken off the table, is recorded. 

 The distance through which the pencil is drawn during the interval is 

 divided into as many equal parts as there are hours in the interval. 

 For example, if the time during which the paper has been on the 

 table is twenty-four hours, and the motion of the pencil in this time 

 has been twelve inches, then each half inch of the length of the dis- 

 tance moved inwards by the pencil will represent an hour. 



To change the paper, the whole shaft with the appended apparatus 

 is lifted up, so that the sheet can be withdrawn and another slid into 

 its place. This is readily effected by means of a light wooden lever of 

 about four feet long; the fulcrum of which is a small wooden block 

 temporarily placed on the edge of the table. One end of this lever, 

 which is forked for the purpose, being placed under the lower end, of the 

 hollow part of the shaft, and the hand applied to the other end, the 

 whole apparatus is elevated sufficiently to allow of the removal of the 

 small iron disc, the withdrawal of the paper, and the insertion of 

 another. To save trouble, and to give a softer surface for the pencil, 

 several layers of paper are put on the table at the same time. 



