444 RIESS ON THE INCANDESCENCE OF 
tain constant charge, bore no relation to the diameters of the 
wires *, 
Cuthbertson disputed the accuracy of Van Marum’s experi- 
ments, and asserted that with equal intensity four times the 
length of wire was melted by a double quantity of electricity, 
and three times the length by one and a half times the quantity 
necessary to melt a single length of wiret. Brook assumed ft 
that the effect of electricity upon wires increased as the squares 
of the quantities of electricity used, so that two jars charged to 
a certain degree would melt a four times longer wire than one 
jar charged to the same degree. Singer§ admits the law of the 
squares for moderate lengths of wire only, as with longer wires 
a portion of the electricity collected in the battery is lost. It is 
also stated that a certain quantity of electricity will melt the same 
length of wire, whether it be accumulated in one or two jars. 
A discussion of these statements, no single one of which can 
be valid in all cases, is for this reason impossible, because no 
mention has been made of the connecting circuit that was used, 
that is, of that part of the wire which was not melted. At the 
time that those experiments were made, an opinion was preva- 
lent that the effect of the electrical battery was solely due to the 
quantity of electricity and to the number and condition of the 
jars that were employed, an opinion which, although it has been 
occasionally repeated in modern times, calls for no express re- 
futation, as every well-conducted Experiment with electricity in 
motion at once disproves it. 
The laws of incandescence can be expressed in the simplest 
manner by the increase of temperature in a wire of constant 
dimensions included with the incandescent wire in the connect- 
ing circuit. In all the following experiments, therefore, I in- 
serted an electrical thermometer in the connecting circuit, the 
increase in temperature of which was observed. The platina 
wire of the thermometer was necessarily chosen of such a thick- 
ness as to remain uninjured on the application of the most 
powerful discharges. In order to obtain an equally sure indi- 
cation for discharges of very different intensities, the same instru- 
ment could not be used for every experiment: I made use of 
* Beschreibung, &c. Erste Fortsetzung, p. 9. 
+ Gilbert’s Annalen, vol. iii. p. 13. 
+ New Experiments in Electricity, Encyclop. Metropolit. Lond. 1830. Elec- 
tric. p. 116. 
§ Elemente der Elektricitatslehre. Breslau, 1819, p. 116, 117. 
