68 H. F. Blariford— Van Bysselbcrglie Meteorograph. [April, 



A spring, which the mechanism, set in motion by the clockwork, causes to 

 ascend and descend in a direction parallel with the axis of the cylinder, 

 comes in contact with the projecting portion, the breadth of which is the 

 greater the more rain has entered the gauge. During this contact, the 

 regulating current passes, cutting off the circuit of the engraving current, 

 and setting free the graver, which records a line on the plate correspond- 

 ing to the length of the cylindrical surface in contact with the spring. 



Next come the wind directions given by the anemometer. In general 

 construction, the anemometer resembles that of Beckley. The direction of 

 the wind is given by two windmill regulators, which cause to revolve a 

 plate forming the cover of a flat cylindrical box. The plate is metallic 

 and presses on eight insulated springs, set at the eight principal divisions 

 of the compass, and connected with eight wires which lead to the recording 

 apparatus below. There is also a ninth wire always in metallic connection 

 with the revolving plate, and the regulating current passes into the upper 

 plate and down by 6 or 7 of the direction springs and their wires whenever the 

 anemometer wires are brought into circuit by the action of the clockwork. 

 It is never completed through the whole 8 springs. In the upper plate, 

 opposite to the pointer which indicates the wind direction, is let in an 

 insulating piece of glass, and this is always in contact with one and some- 

 times with two adjacent springs, through which therefore, the communi- 

 cation is cut off. 



The eight direction wires communicate with eight small studs ; over 

 which the clockwork mechanism causes a small spring to pass, making 

 contact successively. The regulating current, passing through these and 

 acting in the manner already described, allows the graver to make a short 

 mark corresponding to each of them, with the exception of that one (or two) 

 thrown out of circuit by the plate of the anemometer. 



Next comes the barometer, and in the case of this instrument, M. 

 Von Eysselberghe has adopted a very beautiful contrivance which dis- 

 penses with the usual corrections for temperature, and enables the barome- 

 ter to give at once its reduced or corrected value. The principle is dis- 

 cussed by M. Van Rysselberghe in his original paper in the volume of 

 the Bulletins de l'Academie Koyale de Bruxelles for 1873 ; and I need only 

 describe it in general terms, by saying that in a syphon barometer such 

 as is used in the meteorograph, the quantity of mercury in the instrument 

 may be so adjusted to the diameter of the tube, that the level of the 

 mercury in the shorter or open arm of the tube is unaffected by changes 

 of temperature. In the open arm of the tube, therefore, the changes of 

 level take place under changes of pressure only. The reading of the baro- 

 meter is communicated by an arrangement similar to that already described 

 in the case of the thermometers ; viz., by a steel cylindrical probe which 



