16 
1st, Whether the melting point of different specimens 
of paraffin is the same. 
2nd, Whether that of the same specimen remains the 
same. 
The method of observation adopted in these experiments 
was as follows. The thermometer had its stem fitted into 
the cork of a colourless glass flask so that when the flask 
was corked the bulb was in the centre of the flask, the ex- 
tremity of the mercurial column appearing during the 
experiment slightly above the cork. The flask was kept 
heated to a point slightly below that of the melting point 
of paraffin. The bulb of the thermometer was then dipped 
for a few seconds into some melted paraffin a few degrees 
above its melting point, and while covered with a fluid 
coating of paraffin was replaced in the centre of the flask. 
The flask being onty a very little colder than the bulb, the 
cooling was then very slow. 
The instrument was placed so that the reflected image of 
the bar of a window was seen distinctly in the mercury of 
the bulb through the liquid paraffin. One observer carefully 
scrutinised this reflected image by a lens, while another 
watched the downward progress of the column of mercury in 
the stem of the thermometer. As soon as the observer scru- 
tinising the image observed a want of definition produced by 
incipient freezing, he noted the circumstance to his col- 
league watching the column, and thus the exact reading at 
which freezing began was ascertained. It was found easily 
possible to ascertain this point to one tenth of a degree 
Centigrade. Four or five separate observations were gene- 
rally taken, before each of which the thermometer was 
re -dipped into the melted paraffin. 
In case of any change taking place in the zero of the 
thermometer while the experiments were in progress, the 
instrument was tried in melting ice before each experiment. 
