54 NEGRETTI AND ZAMBRA, HOLBORN YIADUCT, E.G., 



end C, and in this position the temperature can be noted. The engraving, 

 fig. 63, shows the thermometer after it has been inverted. 



This reading may be taken at any time after the thermometer has been 

 turned over, for the quantity of mercury in the lower part of the stem, which 

 gives the reading, is too small to be sensibly influenced by a change of tempera- 

 ture, while that in the bulb will continue to contract with greater cold and to 

 expand with greater heat, and in the latter case some mercury will pass the 

 contraction A, and may fall down and lodge at B, but it cannot go further so 

 long as the bulb is upward, and thus the temperature to be read off will not be 

 vitiated. It must be clearly understood that the thermometer is only intended 

 to give the temperature at the time when it turned over. The divisions and 

 figures are engraved upon the stem of these thermometers.* 



It will be seen in the accompanying drawing that twelve thermometers are 

 mounted on the stand ; each one is sustained upon a metal arm in such a man- 

 ner that it will fall over and become inverted by the release of a stop or detent 

 from the joint action of the clock and galvanic battery. 



In the drawing, six of the twelve thermometers are shown inverted, the 

 bulbs being upwards, the clock at each of the six successive hours having made 

 contact and completed the galvanic circuit, and by the action of an electro- 

 magnet released the detents, and allowed the thermometers to fall over and 

 record the temperature for that moment. This action is produced by simple 

 mechanism on the back of the clock dial, the contact being made at each hour 

 It will be evident that the thermometers could be made to record half-hourly, 

 or they might, by increasing the number, be made to register every fifteen 

 minutes, or less, the only limit being the number of thermometers used. 



When the thermometers are all reversed, the readings may be quickly 

 taken and the thermometers re-turned to their original positions, bulbs down- 

 wards. 



Attached to the back of the clock dial, and in its centre, is a disc of ebonite, 

 about two inches in diameter, with a hole in the centre to allow the spindle to 

 pass on which the clock hands are fixed. Round the edge of this disc are 

 twelve platina studs, one being opposite each hour on the clock dial ; each stud 

 is separately connected to one of twelve terminals in the order of 1 to 12 

 at back of clock, viz. : The stud opposite 12 o'clock on the dial is carried to No. 

 12 terminal, &c., &c. Immediately behind the hour hand, at the back of the 

 dial, and attached to the same spindle, is a metal spring which touches each 

 stud in succession as the hour hand travels round. This spring is not 

 insulated from the metal work of the clock ; consequently the current runs to 

 the clock. 



* These Thermometers are divided with either Fahrenheit or Centigrade Scales, and their number may 

 be increased to special order. 



