338 Proceedings of the Royal Society 
In the summer of 1864, Mr Eeilly revisited the chain of Mont 
Blanc with his map and theodolite, and was able to improve the 
former at several points formerly obscure, particularly in the neigh- 
bourhood of the southern glacier of Miage. He gained great 
additional insight into the details of the very heart of the wildest 
parts of the range by ascending, all for the first time, three lofty 
peaks previously unattained, the Aiguille d’Argentiere and the Mon- 
delant to the eastward, and the magnificent Aiguille de Trelatete, 
which closely approaches Mont Blanc on the south-west. In 
addition to this, he traversed this most difficult chain in two new 
directions from the Jardin to the G-lacier of Triolet on the Italian 
side, and again from the Col de Miage to the glacier of Bossons by 
the Dome de G-oute. 
Altogether, Mr Eeilly has achieved the remarkable distinction 
of presenting for the first time to the eye of the tourist and the 
physical geographer a correct and -skilful delineation of the most 
remarkable and most elevated mountain chain in Europe. Three 
different states, France, Sardinia, and Switzerland, divide the 
chain between them. Of these, Switzerland alone has given any- 
thing to the world in the least degree worthy of the spot, and that 
unfortunately only embraces a secondary part. It is a singular 
chance which has enabled a British amateur to produce a work so 
creditable and so long desired. Let us hope that no delay will 
take place in its publication. 
4. On the Solution of Perigal’s Problem concerning the 
contact of Epicycloidal Curves. By E. Sang, Esq. 
If the centre of a revolving wheel be carried with a uniform 
velocity, along a line ; and if a tracing-point be fixed to an arm of 
the wheel, that point will trace out a curved line ; to which the 
general name cycloid or trochoid has been given ; the former appel- 
lation being often restricted to those cases in which the centre of 
the wheel moves in a straight line, while the name epicycloid is 
given when the same centre moves along the circumference of a 
circle. 
When the tracing-point is placed very close to the centre of the 
wheel, the curve is slightly undulated ; the depth of the waves. 
