me 
360 
THE HALL PHENOMENON IN LIQUIDS. 
PROFESSOR ANTONIO RoITr publishes (Atti ace. 
lincei, xii. 397) under the above title the results of 
some experiments he has made. In preparing him- 
self for his work, he repeated some of the ordinary 
experiments upon this phenomenon in metals: and 
the results, which contain nothing new, are shown 
in several diagrams. He devised one new experi- 
ment, however, which shows, as he thinks, that the 
effect he is investigating is not due to a direct ac- 
tion of the magnetic field upon the electric current 
per se. As the opinion thus reached by Professor 
Roiti must have been held two or three years by all 
who have given special attention to the matter, it is 
hardly worth while to inquire whether his new ex- 
periment is conclusive in itself. 
In experimenting with liquids, Professor Roiti was 
unsuccessful in his main object, no effect similar to 
the well-known action in metals being detected. 
It did appear, however, that the magnet, acting 
upon a solution of sulphate of zine of given strength, 
was able to produce a change in the electric conduc- 
tivity of the solution, the sign of which depended 
upon the direction of the magnetic force, the current 
in the liquid, and the degree of concentration of the 
solution. Thus, in a solution less concentrated than 
that which possesses the maximum electric conduc- 
tivity, the effect was in a certain direction; while the 
opposite effect was produced, under the same condi- 
tions of current and magnetic force, in a solution 
having a concentration greater than that correspond- 
ing to this maximum. In a saturated solution no 
similar effect was observed. 
Professor Roiti attributes this behavior of the non- 
saturated solutions to a want of homogeneity in the 
liquids, which become stirred up by the ponderomo- 
tive electromagnetic action. He makes several ex- 
periments tending to support this opinion. In a 
solution of ferric ‘chloride (cloruro ferrico), of spe- 
cific gravity 1.34, effects were obtained similar to 
those found with the dilute solution of sulphate of 
zinc. In a thin layer of mercury no similar effect 
was detected. 
The examination of liquids with the view of de- 
tecting a ‘rotational effect’ similar to that observed 
in metals was probably first suggested in print by 
Kttingshausen.! The difficulties of the investigation 
were obviously great, however; and Professor Roiti 
appears to be the only experimenter who has yet un- 
dertaken it. 
His account of his experiments is open to criticism 
in this respect: that it does not give sufficient data in 
regard to intensity of magnetic field, etc., to enable 
the reader to determine how severely the liquids were 
tested for the presence of the effect which gives the 
title to his article. 
Moreover, he seems to have made a point of placing 
his side-connections unsymmetrically, so as to have, 
independently of the magnet’s action, a considerable 
‘derived’ current, — an arrangement which enabled 
him to discover the effect described above, but which, 
1 Anz. akad. wissensch. Wien, March, 1880. 
SCIENCE. 
[Vot. IIL., No. 59. 
on that very account, should be studiously avoided 
in seeking for the phenomenon he was trying to 
detect. 
Professor Roiti’s ultimate object in beginning this 
investigation was to determine whether the trans- 
verse or ‘rotational’ effect would in liquids corre- 
spond to the magnetic rotation of the plane of 
polarization of light. Of course, no conclusion what- 
ever upon this point can be drawn from the account 
given of his work and its results. And, even if his 
experiments had been entirely successful in revealing 
the effect looked for, it would be necessary to exer- 
cise caution in applying results so obtained to the 
case of the rotation of light. In the liquids, as here 
examined, the particles have time to fully adjust — 
themselves, in position and motion, to the require- 
ments of the magnetic force and the electric current 
to which they are subjected; while in the phenome- 
non of light, assumed to be electromagnetic in char- 
acter, the mere inertia of the particles of the liquid 
must play an important part in the action of forces, 
which are reversed a countless number of times every 
second. 
‘In the Comptes rendus of Sept. 17, 1888, Professor 
Righi states that he has found the Hall effect in bis- 
muth to be of the same sense as in gold, but about 
five thousand times greater than in the latter metal. 
He obtains a very marked action in bismuth by use 
of an ordinary bar-magnet, and believes that he can 
produce a perceptible effect by the action of the 
earth’s magnetism. 
JANET’S THEORY OF MORALS. 
The theory of morals. By PauL JANET. ‘Trans- 
lated from the latest French edition [by Mary 
CHAPMAN]. New York, Charles Scribner’s Sons, 
1883. 10+ 490 p. 8°. 
Ir books on ethics are to be noticed at all 
in a scientific journal, they might be, as a rule, 
safely classified under the head of fossils. No 
literature deals with a subject which would 
seem to be more living; yet no literature is, on 
the whole, more desiccated and dead. Human 
conduct, with all its infinite variety of stand- 
ards and impulses, with all its marvellous in- 
terworking of passions and emotions, with all 
its pressing and personal problems, conflicts, 
and obligations — what subject would seem to 
stimulate students to greater vividness, pic- 
turesqueness, or incisiveness of treatment? 
Every man is in his own way an ethical phi- 
losopher. No one can escape thinking about 
the right principles of his conduct. Books on 
this subject address the largest possible audi- 
ence on the one unavoidable subject of reflec- 
tion. And yet there seems to be some subtile 
‘influence which dries up even literary instincts 
when they approach this theme and which 
There 
makes even brilliant writers wearisome. 
