fossiliferous in the lower part of the St. Lawrence river ; 
further inland it has not been observed to contain fossils, 
From the author’s description of the boulder-clay as seen 
at low levels in Canada, we think that deposit more 
closely resembles some of the maritime fossiliferous 
stony clays of Britain than our Till or lower boulder-clay. 
Dr. Dawson seems to have satisfied himself that the “ real 
cause” of the excavation of the American lakes “was ob- 
viously the flowing of cold currents over the American land 
during its submergence.” He also thinks that “ the fiords 
on coasts, like the deep lateral valleys of mountains, are 
evidences of the action of waves, rather than that of ice.” 
No glacialist, as far as we know, holds the extravagant 
belief that fiords have been cut out by ice. They are un- 
doubtedly submerged valleys, and were hollowed out by 
streams and other atmospheric influences in ages long 
anterior to the glacial epoch. But however much we may 
differ from Dr. Dawson in some of his conclusions, there 
can be no doubt that he has added very considerably to 
our knowledge of American glacial deposits, and we cor- 
dially recommend the perusal of his “ Notes” to our geo- 
logical readers. 
LETTERS TO THE EDITOR 
[ The Editor does not hold himself responsible for opinions expressed 
by his correspondents. No notice is taken of anonymous 
communications. } 
The Invention of the Water-Air-Pump 
STATEMENT BY Pror. BUNSEN* 
** A letter addressed to me by Dr. Sprengel, under date of 
November 1, 1872, in which he says: ‘ Perhaps it will not have 
escaped your observation, that the invention of the water-air- 
pump, which you have constructed after the principle of my 
mercury air-pump, according to your paper published in 1868 on 
the washing of precipitates, is almost everywhere attributed to 
you,’ induces me to make the following statement : * 
‘The interesting discovery, that by means of columns of 
liquids flowing downwards a more perfect vacuum can be pro- 
duced, than was possible by the air-pumps hitherto in use, 
belongs solely and only to Dr. Sprengel. He in his researches 
on the vacuum (Journal of the Chemical Society, January 1865) 
brings prominently forward, that water is from a practical point 
of view the only liquid which could come into consideration as 
a substitute for mercury used in the instrument described by him ; 
and that it is not unlikely that such an iestrument, adapted for 
water, might possess advantages which air-pumps of other 
constructions have not, particularly in hilly countries, where the 
large volume of a natural waterfall might be rendered available. 
In the theoretical considerations on the action of his instrument, 
which immediately follows the above, it is noticed, that it is 
simply the reverse of the Trompe, with this addition, that the 
supply of air is limited, while that in the Trompe is unlimited. 
“Tf in the face of these facts, which are open to all, anyone 
attributes to me, as I must conclude from Dr. Sprengel’s letter, a 
share in his discovery, I can regret this only all the more keenly, 
as in my treatise on the new method of filtration I could not 
possibly have expressed myself with regard to Dr. Sprengel’s 
claims more loyally and precisely than I have done. There, I 
have stated expressly, that I have constructed the pump used for 
filtrations and described by me in detail, after the principle of 
Sprengel’s mercury-air-pump. It was the only apparatus of the 
kind which Dr. Sprengel described, consequently the one to 
which alone I could refer. **R, BUNSEN 
“‘ Heidelberg, Nov. 5, 1872” 
Expressing my best thanks to Prof. Bunsen for the above 
statement, 1 beg to add, that since 1860 I have been using for 
laboratory purposes a water-trompe, as described by me in 
Posgendorff's Annalen for 1861, vol. cxii., which (by reversing 
the action) led me in 1863 to the new method of air-rarefaction. 
Water was the first liquid, which I used in my first pump, con- 
structed during the sammer of 1863. But the fallacies arising 
from the tension of aqueous vapour and from the air absorbed in 
authorised by Prof. Bunsen. 
NATURE 
241 
water, as well as the’ inconvenience of having to provide for the 
requisite fall, caused me to discontinue the use of water, and to 
substitute in its stead mercury as the most suitable liquid for 
establishing ¢4e truth, which I had recognised by means of a 
water-air-pump with an insufficient fall. My paper of 1865 was 
written with reference to a// liquids ; in fact, on p. 15 (rendered 
prominent by italics) I summed up thus :— 
“* The main fact which I have established in this paper may 
be shortly stated to be that, 7/ a liguid be allowed to run down a 
tube, to the upper part of which a receiver is attached by means of 
a lateral tube, and if the height at which the receiver is attached 
be not less than that of the column of the liquid which can be 
supported by the atmospheric pressure, a vacuum will be formed in 
the receiver minus the tension of the liquid employed.” 
I regret that the obviousness of the matter led me to refrain 
from expressing myself in a more detailed manner, believing, as 
I still believe, that what I wrote sufficiently described the con- 
struction of the water-air-pump. 
In conclusion Mr. Johnson’s aspirator * for establishing a 
current of air ought to be mentioned here. It was recognised 
by Prof. Hofmann’ to act on the principle of the trompe, and 
of course might have served as an air-pump, had it been noticed 
at the time that the instrument would furnish the means of 
creating a vacuum. And I may also draw attention to the tubet 
of a vacuum-pan, through which the water is made to escape, 
which has served to condense the steam of the boiling liquid. 
This no doubt would in like manner have served as a complete 
water-air-pump, but it does not appear that its use as such was 
discovered. H. SPRENGEL 
London, Jan. 22, 1873 
Kant on the Retarded Rotation of Planets and Satellites 
Ir is now recognised that the tides are necessarily lengthening 
the day; but the history of this recognitionseems to be incom- 
plete. ‘‘ It appears,” says Mr. Tait in his ‘‘ Thermodynamics,” 
p. 86, ‘‘that the first suggestion of such an effect is due to 
Kant.” Mr, Stewart speaks more positively (‘‘On Heat,” 
Pp» 356), but adds that Mayer ‘‘ was the first to give his conclu. 
sions general publicity.” 
The following are the facts with respect to Kant, as they are 
to be found in Rosenkranz and Schubert’s edition of his works, 
part vi. pp. vii. 3-12. The Berlin Academy of Sciences had pro- 
posed, as the subject of a prize essay for 1754, the questions 
whether the length of day and night had changed, and if so, 
what the cause could be and how this was to be ascertained. 
Kant did not compete ; apparently he was dissatisfied, as well 
he might be, with his attempt to estimate the possible amount of 
retardation ; but he published his views in a Konigsberg weekly 
paper. 
It is of some interest to compare Kant’s position with our own. 
In the first place, he expresses himself with almost entire gene- 
rality. He does not speak merely of the tides, but says that the 
rotation of any planet is necessarily retarded if it contains a con- 
siderable amount of fluid. Kant knew as well as we do that the 
considerableness (that is the magnitude) of the cause affected only 
the magnitude (and not the bare reality) of the effect ; so there is 
nothing to be added to his statement of the condition of retarda- 
tion but what our own writers do not seem to think worth 
adding, namely the energy dissipated in consequence of the im- 
perfect rigidity and elasticity of the solid parts of the planet. 
Again, with respect to the final result, Kant makes two state- 
ments, which, if literally contradictory, yet taken together go to 
show the fulness of his knowledge. First he says the rotation 
must ultimately cease ; further on that it must diminish till it is 
equal to the revolution of the moon, so that the earth will con- 
stantly face the moon, as the moon now constantly faces the 
earth. The essay bears marks of hasty writing; and it seems 
clear that the latter statement is only intended for that part of the 
effect which is due to the moon. The former may be intended 
to affirm the ultimate abolition of the solar day ; if it means 
much more (as it ought) I presumeit is inconsistent with Kant’s 
express rejection of the hypothesis of an interplanetary resisting 
medium. 
On the other hand, Kant betrays no suspicion of the reaction 
upon the disturbing bodies, and the consequent lengthening of 
the month and year. And in speculating on the possibility of 
* Quarterly Yournal of the Chemical Society, vol. iv. p. 186, 1852. 
+ Ibid 
* Translated from Ann. Chem. Pharm. vol.clxv, p. 159, by H. Sprengel, Bs “ Elements of Physics,” by Neil Arnott, M.D, (Longmans,) 3rd edit, 
ondon, 1823. 
