of Edinburgh, Session 1864-65. 
335 
Tuesday, 3c? January 1865. 
Professor CHEISTISON, V.P., in the Chair. 
The Chairman delivered the Makdougall-Brishane Medal, which 
had been awarded to Mr J. Denis Macdonald, E.N. 
The following Communications were read : — 
1. A Map of Taranaki, New Zealand, executed by a Maori, 
was exhibited, and remarks on it by Dr Lauder Lindsay 
were communicated by Mr A. Keith Johnston. 
2. Professor Tait read a note on the various investigations of 
the Law of Frequency of Error ; in which he pointed out that the 
difficulty was really a logical, not an analytical one ; and showed 
how from a priori principles, somewhat different from those of 
Laplace, it was easy to obtain the received result without the 
formidable analysis of Laplace and Poisson. Some curious con- 
sequences were shown to follow from the principles adopted. 
3. Notice respecting Mr Eeilly’s Topographical Survey of 
the Chain of Mont Blanc. By Principal Forbes. 
On the 6th February 1843, or almost twenty-two years ago, I 
had the honour of laying before this Society an account of a topo- 
graphical survey of the Mer de Glace of Chamouni and its neigh- 
bourhood, together with the detailed map founded upon it, being 
probably the first map of a glacier on such a scale ever constructed. 
Since that time I have never ceased to interest myself in the im- 
provement and extension of this survey. Two subsequent editions 
of the map appeared, containing the results of my continued ob- 
servations with the theodolite in 1843, 1844, 1846, and 1850. The 
last edition (on a reduced scale), in 1853, included the whole of the 
glacier of Bossons and the results of an extended triangulation, in 
which the Flegere and the Breven formed the extremities of a new 
base connected with the stations L, M, and I of my former survey. 
Since 1851 the state of my health has put a bar in the way of 
any farther personal exertions in elucidating the topography of the 
