462 



XEGRETTI AND ZAMBEA, HOLBOEN VIADUCT, E.C., 



2805 Electrical Indicating Signal Bell (fig. 2805). When the alarm is put into 

 action by the electrical current a revolving disc is moved, pointing out 

 to the observer the particular bell that has been sounded : where several 

 bells are in use at a station this is an important addition to the instrument. 



Price 220 



These Bells can be very economically fitted up in connection with one or more 

 of the Leclanche or Bichromate Bottle Batteries (figs. 2551 and 2554). A simple 

 immersion of the elements of the Bichromate Battery in the solution for a second, 

 being sufficient to ring a bell to a considerable distance. The Leclanche has, 

 however, been found the most useful form of battery for this work ; it being 

 most simple and cleanly in use (no strong or corrosive acid being required), and 

 the elements remain unimpaired for a very long period. See description, page 433. 



2806 NEGRETTI AND ZAMBBA'S ELECTRIC THERMOMETER, 

 Which will indicate, by ringing a Bell, when the Temperature in a Greenhouse 

 falls below or rises above the point at which injury would be caused to plants, &c. ? 

 the Thermometer being placed in the Greenhouse, and the Bell in the gardener's 

 cottage, or at any other convenient spot. It also indicates present temperature, as, 

 an ordinary Thermometer, and can be used as an efficient Fire Alarm in Warehouses 

 or in Private Dwellings. Price, including Bell, Battery, Thermometer, and 50 feet 



of Double Connecting Wire (fig. 2806) 1 10 



Extra Double Wire, 2d. per Yard. 



These Thermometers can be constructed to ring a bell at two or more different 

 Temperatures, should such be required, at a slightly increased cost. 



ELECTRIC BELLS. 



2807 Electric Bells, on Polished Mahogany Mounting, horizontal or vertical action. 

 For general House or Telegraph use (fig. 2807). 



Trembling. 



Bell 2 in. each 10s. 



3 12s. 



16s. 

 21s. 



28s. 



Estimates given for Telegraph or Household Signal Bells, Electrical Alarm 

 Apparatus, fittings, &c., upon receipt of particulars. 



