264 
took for spiral fibres, I presume; but they are only visible in 
places and not in all hairs. I confess that at present I am 
a sceptic on this point. 
With apologies for this hasty letter, 
I am, Dear Sir, 
Your most obedient servant, 
J. Mitchell, Captain, 
Superintendent Madras Museum. 
Professor Roscoe read the foildiving extract from a letter 
which he had received from Professor Boettger, of Frankfort, 
respecting the occurrence of the salts of Caesium, Rubidium 
and Thallium together, in the salt obtained by evaporating 
the mineral water of Nauheim, near Frankfort. 
“ The Nauheim salt is a highly valuable substance, as being 
perhaps the only material from which Caesium can be obtained 
in quantity. According to my experiments, lewt. of this 
salt yields lib. of double chloride of Caesium and Platinum, 
containing small quantities of the Rubidium and Thallium 
double salt. At my special request the “ Kurfiirstliche 
Salzamt” in Nauheim has arranged to sell this evaporated 
salt, packing included, at the exceedingly low rate of one 
thaler (3s.) per cwt. In my spectrum investigations I almost 
invariably employ a flame of hydrogen in place of the common 
Bunsen’s lamp, as by this means I obtain a higher tempera- 
ture, and the lines appear therefore more distinct. The 
spectrunfof the triple platinum-chloride of Cresium, Rubidium, 
and Thallium thus obtained exhibits in the first place the 
well-defined emerald green lino of Thallium, soon afterwards 
the two brilliant blue (hesium lines appear close together, 
then the very broad and ill-denncd blue bands of Rubidium 
arc seen, as well as the two narrow red lines characteristic of 
this metal. 
“ I have lately discovered the presence of Thallium notonlv 
in many other mineral waters, but also in the vegetable 
