818 
tabular summary of the behavior of the most 
important indicators toward the more common 
acids and bases. 
On the whole, the book is likely to prove 
useful in the laboratory for reference, as it is 
carefully compiled and brings into a compact 
and systematized form a great mass of scattered 
detail. Although 75 per cent. of the indicators 
and test papers recorded would probably never 
be used by the average chemist, yet, in special 
eases, where the ordinary indicators fail, it may 
prove a great convenience to have at hand such 
a compilation from which a suitable one may be 
selected. The educational value of the book, 
however, might in many cases be increased by 
the use of graphic formulas, especially in several 
of the syntheses which the author represents 
merely by equations. 
The book is of a convenient size and attrac- 
tive in form, the subject-matter is well arranged, 
printed on good paper with very clear type, but 
the proof-reading has been only fairly well done. 
M. T. B. 
Zur Analyse der Unterschiedsempfindlichkeit. By 
LILLIE J. Martin und G. E. MULurEr. 
Leipzig, J. A. Barth. 1899. Pp. vii+ 2383. 
M. 7.50. 
It is a psychological sign of the times that 
this work on the perception of weight does not 
in the least concern itself with Weber’s law, 
but leaves that issue entirely aside in order to 
consider the psychological and physiological 
elements in the process. Instead of looking for 
the bare statistical result of a large number of 
judgments, it asks how a judgment is carried out. 
Accepting as a fundamental answer the theory 
of Muller and Schumann—according to which 
the process consists in lifting with equal mus- 
cular force the two objects to be compared, and 
inferring their relative weights from their re- 
sulting movements—accepting this theory with- 
out serious discussion, the authors seek for 
minor factors in the process. Their method is 
two-fold: to collect introspective observations 
made during the experiments, and to vary the 
conditions and contrast the statistical results. 
By these methods they have detected the fol- 
lowing factors : 
First, fatigue and its opposite, namely, excita- 
SCIENCE. 
[N.S. Von. X. No. 257. 
tion or ‘Bahnung.’ It may happen that lifting 
the first of a pair of weights fatigues the motor 
centers ; if so the energy of the second lift will 
involuntarily be less than that of the first, and 
the second weight will seem heavier than it is.. 
In other conditions of the neuro-muscular sys- 
tem, lifting the first weight does not fatigue but. 
stimulates; the second lift is then more ener- 
getic than the first, and the second weight feels 
correspondingly lighter. This theory—for it iS: 
not so well established as the other points made 
by the authors—is advanced in explanation of 
the ‘ time-error.’ 
Many judgments, though purporting to con- 
sist in the comparison of two given weights, 
were found to be something quite different. 
Often they were based on ‘side-comparisons.’ 
The actual comparison was not between the two: 
weights given to be compared, but between one 
of them and the corresponding weight of the 
preceding pair. Though this seems an indirect 
and far-fetched manner of judging, it is often 
more readily adopted than the direct compar- 
ison. And in other cases no genuine comparison 
at all takes place, but the judgment is based on 
an impression of the absolute weight of one of the 
lifted objects. After growing accustomed to the: 
series of weights used in an experiment and 
getting one’s movements adjusted to the aver- 
age run of those weights, one often finds that a 
weight on being lifted feels light, or feels heavy. 
This feeling is not a definite comparison of the 
given weight with the average ; it is a mere im- 
pression, yet often very reliable. The impres- 
sion is stronger the more the given weight differs 
from the average ; which means that the easiest 
and most confident and correct judgments are 
the most apt to be determined by the mere im- 
pression, and the least apt to be genuine com- 
parisons. Practice by no means eliminates this 
way of judging; on the contrary, the best 
demonstrated effect of practice was to increase 
the dependence on these impressions. 
The impression of absolute weight operates 
differently in two classes of persons. Those of 
strong muscles and energetic movements are 
more subject to the impression of lightness ; the 
less energetic to the impression of heaviness. 
A large part of the monograph is occupied 
with an attempt to follow in detail the combined 
