10 
be serviceable for solving inverse questions, such as what 
must be the law of density in order that the intensity of 
the light may be a given function of the distance traversed. 
As a particular instance, the density is determined in order 
that the intensity may vary as the inverse nth. power of the 
distance. 
“The Death-age in Langwies (Switzerland),” drawn up 
by Arthur Wm. Waters, F.G.S., F.L.S. 
Many visitors feeling that the growth of Davos has been 
too rapid, have been anxious to see other places similarly 
situated, at a high level, tried as winter resorts for con- 
sumptive patients, and many competent authorities have 
thought that the position of Arosa (6000 feet) at the upper 
end of the Schanfigg valley was very favourable. I therefore 
went over this spring to see it. 
When visiting it I took the opportunity of drawing up 
a table of the age at death in Langwies (4519 feet above 
sea level), a village at the lower end of the Schanfigg valley. 
This Schanfigg valley is parallel with the valley of Davos and 
also with the Engadine, and as I some years ago published 
the death age of the inhabitants of Davos (Klimatolog. 
Notizen ii. Winter im Hochgebrige, Basel 1871) and Dr. 
Ludwig published those of the Engadine (Das Oberengadin 
von Dr. J. M. Ludwig, 1877), we have now figures for these 
three neighbouring valleys. 
I only used the figures since 1800 A.D., because the ages 
in the last century did not seem to have been kept with 
quite as much fulness as lately. 
With regard to Davos I quote a second table which is the 
more valuable (although only relating to a smaller number) 
on account of the first table containing the register of a few 
who died away from Davos. 
