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approach makes a material difference ; and even the polish 

 of the surfaces, if in contact, produces a disturbing effect. 



A very good instrument has been formed by floating a 

 small bar magnet perpendicularly in water, like a hydro- 

 meter, and placing a coil of wire around it ; or by suspending 

 a bar magnet from one of the arms of a balance, and in like 

 manner placing a coil of wire around it. These instruments 

 possess many of the advantages of the new instrument I 

 produce to you, but are much more expensive and difficult 

 to manage. 



Being engaged in a series of experiments relative to the 

 conduction of voltaic electricity, and requiring a galvano- 

 meter in addition to the instruments I possessed, and not 

 being able to obtain any instruments suitable for my purpose 

 from the makers of philosophical apparatus in the county, I 

 was led to make the galvanometer before us. The construc- 

 tion being new to me, and, as I conceive, combining simplicity 

 of construction with several other advantages, I shall have 

 much pleasure if it be found useful to those engaged in 

 electrical investigations. My instrument consists of about 

 thirty feet of copper wire wrapped with cotton, coiled upon 

 itself, and cemented with shell lac at the end and side, so 

 as to retain its form, having the ends of the wire bent so as 

 to form points at which the coil is suspended in a vertical 

 position. The points of the wire dip into two small cups, 

 drilled into the end of two thick brass wires, which serve 

 as supports for the coil ; a little mercury being put into the 

 cups. Two arms of wire are attached to the coil, on the 

 ends of which a small scale to contain weights is suspended, 

 thus forming a kind of balance, which, when nicely adjusted, 

 is sensible to about the tenth part of a grain. A common 

 permanent horse-shoe magnet is placed within the coil. Con- 

 nexions are made between the electrodes and the supports of 

 the coil by binding screws, or otherwise, as most convenient. 



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