1835] WRITINGS OF JOSEPH HENRY. 97 



13. One of the most singular results in this investigation 

 was first obtained in operating with the large galvanic bat- 

 tery [fig. 2, page 84]. The whole instrument was arranged 

 as a "calorimotor" of eight pairs, and a large spiral con- 

 ductor introduced into the circuit at c d, while a piece of 

 thick copper wire, about five inches long, united the poles at a 

 b. In this state an explosion or loud snap was produced, not 

 onl}' when the contact was broken at the spiral, but also 

 when one end of the short wire, at the other extremity of the 

 apparatus, was drawn from its cup. All the other short 

 movable connectors of the battery gave a similar result. 

 When the spiral was removed from the circuit, and a short 

 wire substituted, no effect of the kind was produced. From 

 this experiment it appears that the influence of the spiral is 

 exerted through at least eight alternations of zinc, acid, and 

 copper, and thus gives to a short wire, at the other extremity 

 of the circuit, the power of producing a spark. 



14. The influence of the coil was likewise manifest when 

 the zinc and copper plates of a single pair were separated 

 from each other to the distance of fourteen inches in a trough 

 without partitions, filled with diluted acid. Although the 

 electrical intensity in this case must have been very low, 

 yet there was but little reduction in the apparent intensity 

 of the spark. 



The spiral conductor produces however little or no in- 

 crease of eff'ect when introduced into a galvanic circuit of 

 considerable intensity. Thus when the large spiral used in 

 experiments seven, eight, &c., was made to connect the 

 poles of two Cruickshanks troughs, each containing fifty-six 

 four inch plates, no greater effect was perceived than with 

 a short thick wire; in both cases in making the contact a 

 feeble spark was given, attended with a slight deflagration 

 of the mercur5^ The batteries at the same time were in 

 sufiiciently intense action to give a disagreeble shock. It is 

 probable however that if the length of the coil were in- 

 creased in some proportion to the increase of intensity, an 

 increased effect would still be produced. 



In operating with the apparatus described in the last exper- 

 7 



