68 

space in your columns to air another subject which I also brought 
before Convocation, with, I am sorry to say, equal want of suc- 
cess, and that is the desirability of modifying the examinations 
for the degree of Bachelor of Science by omitting the biological 
subjects, so as to induce engineering students to take it. At present 
the biological subjects required for the degree, viz., Zoology, Botany, 
Physiology, and Organic Chemistry, are so entirely foreign to the 
studies and requirements of such students that in most cases it is 
scarcely practicable, even if it were desirable, for them to travel so 
far out of their regular line of work, for the purpose of getting 
them up for the Bachelor of Science examination. Such a 
course would be precisely analogous to that which is now pre- 
scribed for medical students proceeding to their M.B. degree, 
who are required to take up those subjects of the B.Sc. examina- 
tion which are cognate to their routine of study, and who then 
branch off to those of a purely professional character. 
Only two objections were urged in Convocation against this 
scheme which are worth consideration. The first was that it 
would tend to lower the standard of the degree by diminishing 
the comprehensiveness of the examination. In order to meet 
this objection I suggested that candidates not wishing to 
take up the biological subjects should be required to sub- 
stitute for them others of a mechanical nature, such as 
Applied Mechanics, Engineering and Architectural Construc- 
tion, and Geometric Drawing, which, as all who have had any 
experience in teaching them know, are quite as capable of being 
made efficient educational tests as those which they would re- 
place. The second objection was, that to make such a change 
would be equivalent to instituting a degree in engineering. That 
this would be the practical result of the suggested alteration I 
am prepared to admit, and it is the object which I had distinctly 
in view in proposing it. What there was in the suggestion to 
provoke the unconcealed opposition of so many of the members 
of Conyocation, I am a loss to imagine, unless it was the illusion 
that the profession of engineering is a less scientific one, and the 
education of its members less worthy of being encouraged, than that 
of the professions of law and medicine, to which so large a pro- 
portion of the London graduates belong. 
For my own part, it seems to me a scandal of no mean gravity 
that, whilst the practice of that profession requires intellectual 
qualifications of the highest order, and a scientific training of the 
widest kind, no means should exist in this country whereby either 
the public should be provided with any guarantee that those who 
practise it possess either of these qualifications, or its practitioners 
themselves should be enabled to give evidence of the fact of 
their own accord. Ido not know of any department of educa- 
tion in which the University of London could, at the present 
time, do more service than in this, and, I trust, there are men in 
its Senate, who, with more breadth of appreciation than the 
majority of Convocation, will give the matter their earnest 
attention, Francis T. BOND 
Hartley Institution, Southampton 

Mechanical Equivalent of Heat 
T AM afraid your publication, without adding the date, of my 
letter last week (which I only saw this morning) puts me in a 
false position in regard to Dr. Joule, inasmuch as it appears to 
ignore a correspondence of mine with him, which took place 
between the time that letter was written (now a long time since) 
and the time of your publishing it. 
In that correspondence I allowed that Dr. Joule’s theory re- 
mained the same in ils main features, though I thought he 
virtually retracted one statement which I had particularly argued 
against. Dr. Joule, however, did not allow he had made any 
alteration, 
He also informed me that a paper of mine had been read at 
the meeting of the Manchester Literary and Philosophical Society, 
in which I showed (as I believe) in a detailed examination that 
his theory was inconsistent with the results, both of his own and 
of M. Favre’s experiments. Dr. Joule also kindly communicated 
to me the substance of the reply which he had made, but I have 
not seen either in print. Of course the question is one of facts ; 
are facts consistent with the new laws of thermodynamics as 
supposed to have been established during the last twenty years ? 
Tait, in his preface to his Thermodynamics, says : “ The subject 
s one of vast importance, but very few indeed are yet acquainted 
with even its most elementary facts ; and by many of these it is 
not yet accepted as true.” These laws, therefore, can scarcely 
NATURE 


[May 25, 1871 
yet be put on a level with Newton’s laws, even if they should be 
shown to be consistent with facts, which, at least in their present 
form, I believe to be impossible. H. HIGHTON 
May 18 

Mr. Hicuron’s letter in NATURE is almost identical with his 
communication to the Chemical News. My answer is similar to 
that which I sent to the latter publication, viz., that the object of 
my paper in the Proceedings of the Literary and Philosophical 
Society was simply to place the theory of the electro-magnetic 
engine in a form which might prove useful to those who had not 
worked on the subject, and not in any respect to withdraw the 
reasonings in what Mr. Highton is good enough to term my 
“famous paper.” Mr. Highton handsomely acknowledged the 
justice of my note to the Chemical News in a letter addressed to 
me on the 28th ult. JAMEs P. JOULE 

Optical Phenomenon 
In reading over Prof. Clerk Maxwell’s paper on Colour in 
Nature (Vol. iv. p. 13), I was reminded of the following, to 
me, curious phenomenon which was seen by me on several occa- 
sions in the summer and autumn of 18509. 
Whilst standing before a black board} making geome'rical 
figures in white chalk, I was struck by one side of each chalk 
line appearing blue, the remaining half retaining its proper 
white. The cause was at once evident to me, for I found that 
the sun shone fully upon one eye, but not upon the other. By 
closing the eye upon which the sun shone, the chalk marks 
appeared wholly white. Opening the eye again, the half blue, 
half white marks appeared ; then closing the eye upon which the 
sun did xo¢ shine, the whole of the marks appeared a pale blue, 
scarcely so deep in colour as when in contrast with the white. 
By squinting, or forcing the eyes to see double, two sets of marks 
appeared, the one set all blue, the other wholly white. 
Subsequently, with the sun upon both eyes, the whole of the 
marks were blue ; whilst upon another occasion, when the sun 
shone very fully upon both eyes, only the white marks were evi- 
dent ; but shading the eyes by the hand, and allowing a ray to 
fall upon one eye, the usual half blue half white lines appeared. 
On every occasion that I tried the experiment I met with the 
same results, and when I looked away a beautiful orange- 
coloured spot—the complementary colour of the blue, I suppose 
—appeared for some time wherever I looked. What is the 
cause why only the blue rays were visible? and why blue rather 
than red or yellow ? THos, WARD 
Yellow Rain 
THE following notice will perhaps be of some interest to the 
readers of NATURE, In December 1870, after a heavy rain at 
Rosario de Cucuta (New Granada), a great many small round 
specks of a yellow clayish substance were found on the leaves of 
plants that had been exposed to the rain, A sample of this sub- 
stance was sent to Dr. A. Rojas, of this town, who forwarded it 
to me in order to examine it under the microscope. It proved 
to be composed almost entirely of a species of 7riceratium, and 
another of Cosmarium, which must have been carried away by 
a violent storm from their lacustrian abodes, 
Caracas (Venezuela), April 1871 A, ERNST 

The Irish Fern 
My first impulse, on reading the note on this subject in 
Nature for the 4th of May, was to apologise to Mr. Dymond 
for having caused him so much regret by making known a Cornish 
station for this fern. This first impulse was however checked by 
the reflection that something is due to the advancement of the 
study of distributive botany ; and I could scarcely have expected 
even Mr. Dymond to place any very great degree of confidence 
in my bare assertion, unaided by any reference to localities. 
Now that I have done the mischief and made known that the 
Trichomanes is a Cornish plant, and have been corroborated by 
Mr. Dymond, it would be interesting to know whether the writer 
of the note on this fern in the Cheltenham Natural History 
Society’s report found his specimen at the same place, 7.e, at 
St. Knighton’s. EVERARD F, 1M THURN 
in Cornwall 
