March 16, 1871] 
and water, and thus “exactly undo the thermal effect of its 
formation. I trust that in this letter, at least, you will find 
nothing unfit to be published in a scientific journal. 
H. HIGHTon 
P.S. I hope to discuss the question wd voce at the meeting 
of the Manchester Literary and Philosophical Society next week. 

Mr. HIGHTON has very effectively shown the uselessness (to 
him) of my review of his speculations. I wish I could withdraw 
it, and allow his letter to speak for him without any comments 
of mine. When a man can make the remarks he has made on 
Sir W. Thomson’s paper of 1854, his case is hopeless—he is in- 
capable of being taught even by the “grand founders” of the 
science. eguiescat, Your REVIEWER 

Quinary Music 
HAvinG hitherto been under the impression that all the 
varieties of time in music might be regarded as made up of 
groups of two or three, and never having seen a single piece of 
music which in any way contradicted this view, Mr. J. Mullen’s 
letter on “‘Quinary Music” in Nature for the gth inst. sur- 
prised me very much indeed. It is true that sometimes we meet 
with passages in which five notes are to be played in the time of 
four, or seven in six, &c. ; but a piece of music in five time is a 
thing I at least have yet to see, and { should feel obliged to Mr. 
Mullen it he will kindly tell me the name and composer’s name 
of this novelty. Beacon LouGH 

The Experimental and Natural Sciences in Trinity 
College, Dublin 
I TRUS? you will allow me to make a few remarks upon the 
article signed ‘‘ W.” which appeared in your last week’s number. 
In the first place, there are one or two inaccuracies which 
may be corrected. Thus, your correspondent states that a stu- 
dent ‘‘in his third and fourth years must devote himself, to a 
certain extent, to the study of Experimental Physics, including 
heat, electricity, magnetism, and chemistry, and pass examina- 
tions on these subjects, even at the ordinary term examinations.” 
The sophister students are indeed a//owed by the Board to sub- 
stitute such a course for classics, but, it may be added, com- 
paratively very few avail themselves of this permission. Again, 
it is declared that ‘‘the chemical and physical laboratories leave 
nothing to be desired.” No such thing as a “physical labora- 
tory” exists in the University ; and, seeing that it is only lately 
that such things have been introduced at the other side of the 
Channel, it is scarcely likely that we shall have one here for 
some years to come, 
But what I think especially calls for criticism is the general 
tone of the article, leading the reader, as it appears to me, to 
suppose that the Experimental and Natural Sciences occupy a 
high status in Trinity College, Dublin. Now this is far from 
being the case ; there can be no doubt that they are still gene- 
rally looked upon in the University as subjects of quite secondary 
importance. iss 
Dublin, March 14 

Science in Schools 
I sHOULD be greatly obliged if you would kindly let me know 
of any school adapted for young boys whose parents wish to 
give them an education embracing the physical sciences and 
modern languages, on some such plan as that of the Realschule 
of Germany. W. 

Dr. Donkin’s Natural History of the Diatomacez 
THE remarks of “K.” on my review of the above-named 
work (vide NATURE, vol. iii. p. 348) fall under five heads. Allow 
me to briefly notice each. 1. There is a difference of opinion 
between us as to the execution of the plates in Part 1 of Dr. 
Donkin’s work ; my copy came direct from the publishing office, 
it is therefore presumably a fair specimen. I have once more 
examined the plates, as well as shown them to several competent 
judges, and the unanimous verdict of all is that expressed in my 
notice, z.¢, the execution of the plates in this part is disappointing. 
I gave instances of apparent inaccuracy in detail in some of the 
figures. ‘‘K.” passes these by, but cites figures that are accurate ; 
surely there is nothing contradictory in this. My criticism 
related for the most part to the execution of the plates, and I 
NATURE 
~ = eee eee 


387 
confess that even comparing them to those illustrating Dr. 
Donkin’s or Mr. O’Meara’s papers on Diatoms in some of the 
late volumes of the Quart. Yourn. Micr. Sci., 1 would prefer the 
lithographic plates to the engraved ones. 
2. “K.” agrees with me about the synonymy. I agree with 
him as to the difficulty of this portion of the subject, but what 
value would this or any work on species have without synonyms ? 
3. “K.” says the desirability of giving habitats in full is 
questionable, ‘‘three or four localities are sufficient.” Un- 
questionably it is not desirable to give more than three or four 
localities for common forms, but I think it is equally unques- 
tionable that when Dr. Donkin could have given as many 
localities for interesting and not extremely common forms, he 
was wrong not to have done so; and I alluded to the absence of 
Irish localities in the hope of removing an evident defect in an 
otherwise useful work. 
_‘K.” is, without doubt, right in referring the species given 
by him to Gregory, and not to Ehrenberg. I cannot imagine 
how so great a blunder on my part originated. 
5. “K.” asks, “‘who is Cleeve?” Cleve (not Cleeve), next to 
Heiberg of Copenhagen, is one of the best northern investigators 
of the lower Algze. His monograph of the Swedish species of 
the Zygnemacez is well known, and in addition to his papers on 
Desmideze and Oedogonium, he has published “ Diatomaceer 
fran Spetshergen” (1867) and ‘Svenska och Norska Diato- 
maceer” (1868). He naturally follows the arrangement of the 
““Conspect. Crit. Diatom. Danicarum.” It is not without 
interest to observe how well acquainted these botanists are with 
the literature in our language relating to the Diatomacez. 

2 

Lenses for Vision Below Water 
IN a communication on the Dioptrics of Vision which ap- 
peared in your impression of the 15th December last, I described 
a form of air-lens for vision beneath the water. Further ex- 
perience has shown me that the measurements I then gave 
were not so accurate as they might have been. Thus, the radius 
of curvature of the glasses in the air-lens to form a lens witha 
2in. focus in water is not r4in. as first stated, but 1 in. only. 
Again, I somewhat underestimated the magnifying power of 
the anterior lens of our eye, formed by the aqueous humour, 
when I set it down as a lens with a focus of 2 inches. 14 inch 
is more correct. In accordance with this, I find that for the 
most perfect vision under water, we require a glass lens 
of $in. focus in air (in place of 1 in. as formerly stated), or an 
air-lens formed with two segments of a hollow glass globe 13in. 
in diameter, placed concavities outwards. Both these lenses 
have in water a focus 1}in. long. 
These lenses are for fresh water. Sea water having a greater 
refractive power than fresh water, requires for perfect vision a 
somewhat more convex glass-lens and a somewhat /ess concave 
air-lens. I find that an air-lens made with segments of two glass 
globes of the diameter of 2 inches and 1j inches respectively, 
when immersed in sea water forms a lens of I+ in. focus. But I 
should observe that good vision under water is obtained by lenses 
of various magnifying powers, ranging from 1} to 2 inches focus ; 
but for the distinct vision of small text-type under water, the 
higher magnifying power is required, and it also is the best for 
distant vision under water, 
53, Montagu Square R. E, DUDGEON 

Petrography 
THE few English geologists who take an interest in petro- 
graphy will be thankful to Mr. Geikie for the communications 
from him which have appeared in Nature. It is too 
true, as he observes, that our progress in this branch of 
geology has for many years been simply 7z/, but there are 
now manifest signs that this unsatisfactory state of things is 
drawing to a close. Some of our working geologists are quite 
aware of the necessity which exists for the application of the 
microscope to the examination of rocks, and they do not doubt 
that the result will be proportionately as great as it has been in 
other branches of inquiry. f 
It may in the first place be observed that the unsatisfactory 
nomenclature at present in use is due to the fact that a consi- 
derable proportion of the igneous rocks have been named 
without any precise knowledge of their mineralogical compo- 
sition, mere chemical analysis being quite inadequate for the 
solution of the problem ; and now there is an evident tendency 
