ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
119 
Beneden was the oldest of Belgian zoologists, and one of that band of 
pioneers of whom Sven Lovcn is alone now left to us. It is to him 
that we owe much of what is now elementary knowledge with regard to 
the wonderful “ alternations of generations ” exhibited by the Hydroid 
Polyps, and the history of the changes undergone by tapeworms in their 
different hosts. He was devoted to the study of parasitic Crustacea, and 
he was the first to show that Pentastomum is a modified and degraded 
Arachnid. So far we have spoken of his work as a student with the 
Microscopo, but it is not to be forgotten how largely he added to our 
knowledge of the hugest of living creatures — the Cetacea, and the 
admirable use to which he put the opportunities afforded him to study 
the fossil Whales, of which the deposits near Antwerp are so full. 
The Measurement of Light and Colour Sensations.* — Mr. E. M. 
Nelson writes : — Mr. J. W. Lovibond in £ Measurement of Light and 
Colour Sensations,’ deals with an instrument invented and called by 
him a “ Tintometer.” Before describing this instrument, it is important 
to bear in mind that the ground traversed is in the main psychological 
rather than physical, because it is light and colour as appreciated by 
the human eye, that are only taken account of. If, for instance, we look 
at monochromatic light of wave-length -52 //,, we should call it green, 
and would be unable to distinguish it from light passed through a piece 
of green glass. But if we examine by a spectroscope the light trans- 
mitted through the green glass we shall find it composed of blue as well as 
of green light. Thus while there exists an essential difference between 
the two greens the unassisted eye is wholly unable to recognize it. 
It would seem, therefore, that all measurements of light and colour, 
which depend solely for their appreciation on the human eye, must be 
valueless. In other words, such measurements in order to be trust- 
worthy must be on a physical, and not on a psychological basis. 
That this, however, is only a shallow view of the question is amply 
proved in this work, for by means of the “ tintometer ” minute differences 
of colour may be perceived and measured, which are quite beyond the 
range of the spectroscope. To adequately describe the “ tintometer ” 
and its applications would exceed the limit of this note, because intricate 
and complex combinations arise before one has proceeded very far, but 
an elementary idea of the principle which underlies its construction can 
be conveyed in a brief description. 
Pure white diffused daylight, such as that observed in a sea mist, 
can be totally absorbed by passing it through certain thicknesses of red, 
yellow, and blue glass. These red, yellow, and blue glasses are divided 
into arbitrary units, so that an equal number of red, yellow, and blue 
units always yield a neutral tint of a certain depth. 
Although the units are arbitrary they are uniform and recoverable if 
lost; thus they in no wise differ from ordinary measures of length, 
weight, and capacity. The limit of perception is • 006 of a unit. The 
mechanism of the instrument is very simple. A tube is longitudinally 
divided into two halves, through one half the object to be tested is 
viewed, and its colour is matched in the other half by the insertion of 
the requisite number of red, yellow, and blue units. 
* ‘Measurement of Light and Colour Sensations,’ London, 8vo, 1893, 132 pp., 
12 pis. and 13 figs. 
