391 
of Edinburgh, Session 1870 - 71 . 
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I find great difficulty 
in obtain 
ing wires 
of the 
more 
infusible 
metals :- 
—and I 
am therefore endeavouring to make a 
complex 
arrangement for very high temperatures with palladium and two 
very different kinds of platinum. Wires of nickel, cobalt, molyb- 
denum, rhodium, or iridium, or of any one of these, would be of 
immense use to me, and I should be happy to hear from any one 
whether there is a possibility of procuring them. 
2. On Phyllotaxis. 
I was recently led to consider this subject by Professor A. 
Dickson, who showed me some of his beautifully-mounted speci- 
mens, and explained to me the method he employs for the deter- 
mination of the divergence, and of the successive leaves of the 
fundamental spiral or spirals. He referred me to two terribly 
elaborate papers by Bravais,* and I have since met with another 
of a similar character by Naumann.f These papers certainly 
cannot be supposed to present the subject from the simplest point 
of view. I do not doubt that the results I have here arrived at are 
to be found in some form or other in their pages, which are an- 
nounced as completely elucidating the question ; but I have not 
sought for them, my sole object having been to put what seem to me 
the elements of the matter as simply and intelligibly as I could. 
* Annales des Sciences Naturelles, 1839. 
t Poggendorff’s Annalen, 1842. 
