220 Scientific Proceedings, Royal Dublin Society. 
In drawing conclusions from those facts, it is well to show the 
students photographs of the Alps (if not already familiar with the 
appearance of high mountains), and the phenomena observed in 
the experiment impressed upon them as a principal cause of the 
cold on high mountains. They should also, of course, be reminded 
of the moisture upon the carafe of iced water,&c. Young students 
should be made to write down upon dictation pithy statements 
in their note-books as to the leading facts observed and the 
deductions drawn, for such are not able to report the words of a 
speaker. 
It will be seen that the experiment displays all the phenomena 
involved in the dynamical explanation of cold on high mountains, 
save the motion of the winds. 
Flotation of bodies, Archimedes’ principle.—Plane down a piece 
of light pine till it is of a uniform cross-section, a square of 1 cm. 
on the edge. Let it be about 30 cm. in length. Drill a hole in 
one end, and load with lead till it floats upright in water. About 
two-thirds will be immersed. Divide it into centimetres and 
half-centimetres from the loaded end, and varnish it. 
The student weighs this on a balance, and then places it in 
water. Ifit weigh 20°5 grammes, it sinks 20°5 ems. in the water. 
He places a single gramme weight on the upper end: it sinks to 
21:5 ems. He then measures if carefully, and convinces himself 
that each centimetre immersed must displace 1 cub. em. of water. 
But as he has already learned that a cub. cm. of water weighs 
1 gramme, evidently the weight of the water displaced is equal to 
the weight of the floating body, or a floating body displaces its 
own weight of water. 
By making this float hollow, closed with a cork at each end 
(cardboard, varnished, does very well), its use may conveniently 
be extended to proving Archimedes’ principle. In this. case, 
weights may be dropped down the floating tube, removing the 
cork, and will not tend to overturn it. 
Let the student put in weights till anything more will sink it. 
At that moment it displaces ” c.cs., and when he weighs it he finds 
it weighs x grammes. Now it is easy to see that the body will 
not displace any more water when wholly submerged, but the 
weighing has proved that the ultimate displacement produced an 
upwards-directed force equal to the weight of the displaced water. 
