





































er work, the eis under which 
he maximum production of ammonia may be obtained 
‘by the decomposition of coal ; it need scarcely be said 
that the subject is one of the greatest importance, 
having regard both to the great manurial value of the 
uct for agricultural purposes and to the highly 
mpor ~ oh part that it plays in the economics of coal 
misation. The lecture concludes with a brief 
me # of the present position of the synthetic processes 
Bip production of ammonia, the chief protagonists 
g¢ the Haber and the Claude processes ; Prof. Cobb 
ntly holds the view that there is likely to be but 
to choose between the costs of production of 
ia from coal and by synthetic methods, and that 
ris to-day impossible to say on which side the advantage 
ill ultimately rest. 
While each of the lectures is a complete little mono- 
raph in itself, the subjects have been carefully selected, 
0 that the book as a whole covers well a large portion 
f the field included under the comprehensive title of 
e Utilisation of Coal, a subject which is of the 
national importance at the present moment. 
as often been said that British coal has been too 
“ap in the past, and that we accordingly got accus- 
to squandering recklessly our greatest national 
et ; such habits of extravagance, once acquired, are 
easily got rid of, but works like the one before us 
at least the great merit of indicating the right 
ud to a much-needed improvement in this respect. 
H. Louts. 
Astrology of Comets. 
is Brahe Dani; Opera Omnia, Edidit I. L. E. 
Dreye Tomus iv. Pp. 377-524. (Hauniae : 
Libraria Gyldendaliana, 1922.) : 
N these pages Dr. Dreyer has given us an interest- 
‘s ing collection of papers on comets, not hitherto 
sssible to the learned world. After the concluding 
e of the well-known “ De Mundi A2therei recenti- 
s Phaenomenis ” we have a treatise of sixteen 
es in German, now printed for the first time, on the 
et of 1577. Next come nine pages in Latin on the 
let of 1585, printed at Uraniborg in the “ Diarium 
‘ologicum et metheorologicum ” of Elias Olai Cimber 
t 1586, and seven pages in the same language now 
t published on the same comet. These last two 
tises are mainly astrological, as is no small part of 
€ seme on the comet of 1577. 
The largest part of the present fasciculus is, however, 
ecupied with a controversy on comets between 
» Brahe and the Scottish physician John Craig. 
» had sent Craig a copy of his printed but as yet 
a NO. 2780, VOL. 111] 
tet NATURE 
179 
unpublished work, “‘De Mundi . . .” and Craig had 
replied in certain letters which as Dr. Dreyer informs 
us were published by Noltenius in 1737. These 
drew from Tycho an “ Apologetica Responsio,” filling 
sixty pages of the present volume. The work was 
printed and a few copies were sent to friends. It was 
Tycho’s intention to include it along with the whole 
controversy with Craig as a supplement to his “ De 
Mundi . . .,” but his representatives wisely decided to 
let the main treatise go forth by itself. No printed 
copy of the “ Apologetica Responsio”’ has survived, 
and Dr. Dreyer has edited it from a MS. at Copenhagen. 
Craig replied to this work in a treatise entitled ‘* Capnu- 
raniae restinctio,” of which Dr. Dreyer has been able 
to give us a fragment from a Vienna MS. The task of 
replying to this work was ultimately undertaken by 
Kepler, but abandoned by him on Tycho’s death, 
though Kepler’s unfinished reply has since been 
published in his collected works. Dr. Dreyer’s notes 
on the whole volume, including the “De Mundi . . .,” 
occupy the last thirty-two pages of the present 
publication, 
Not the least instructive of these studies are the 
astrological treatises. It will be observed that with 
the exception of the paper written for his assistant, 
Tycho early abandoned the intention of publishing 
them. In an age when nearly all science was based on 
an experience not supported by carefully recorded 
experiments and observations, it was reasonable to 
give to the supposed truths of astrology the same 
respect that was shown to scientific teaching generally. 
Tycho’s astrology is neither fanciful nor arbitrary, but 
professes to regard observation as the test of truth. 
Thus on p. 413 he refuses to decide on the limits of the 
clima of Saturn, because they rest on no sufficiently 
attested experience. On the other hand, he regards it 
as a settled fact that the comet which was seen in Aries 
in 1533 changed the religion,in, Britain and caused 
lasting discord. Whatever value Tycho may have 
attached to such speculations, he could not but feel 
that they were work of a very different class from the 
great astronomical edifice founded on his own observa- 
tions of precision. 
The controversy with Craig is not without its analogies. 
Craig held with Aristotle that objects in the ether were 
immutable, while objects in the elements might suffer 
change, and that temporary phenomena like comets 
must, therefore, be sublunar. Tycho Brahe held that 
from the relative slowness of their motion and the 
absence of perceptible parallax they must be more 
distant than the moon, The question is of the ever 
recurrent type where observations seem to conflict with 
a general principle which has hitherto known no 
exception. 
