8 



HARDWICKE'S SCIENCE-GOSSIP. 



and violet disc looks blue ; a red and blue, purple. 

 Considering the formation of the sensation of orange 

 in this way : the colour produced is indistinguish- 

 able by the eye from the same colour in the spectrum, 

 but whilst the orange beam in the spectrum consists 

 of rays of definite wave-lengths, and is not split up 

 into further colours by passing through another 

 spectroscope, the composite orange beam formed 

 by the mixture of red and yellow rays, consists 

 of rays of quite different wave-length (those corre- 

 sponding to red and yellow), and is again split up 

 into the original colours that formed it on traversing 



the large one. When the colour is a bright and 

 intense one, the white or black must be combined 

 with it, that is, must be subtracted from the other 

 three. The amount of the several colours used can 

 be determined numerically by measuring the angle- 

 included in each coloured sector, and in this way 

 Maxwell obtained his colour equations. 



Maxwell's colour-box is an apparatus by which any 

 two or three portions of the spectrum can be made to- 

 overlap, and the resulting light examined. This is 

 by far the most accurate means of determining colour 

 mixtures. 



ABC 



Re::!. Yel. Gr= Blue. Violet. 



Fig. 2.— Diagram of light reflected from green pigment. (O. N. Rood. 1 



A B C 





Red. 



Yel. 



Gr, 1 . 4 



Bi 





Fig. 3. — Diagram of light relected by green leaves. (O. N. Rood.) 



a spectroscope. In fact it is only the sensation of 

 orange, which is the same as the sensation of red and 

 yellow combined ; or, the mixture of red and yellow 

 rays to form an orange sensation is a physiological 

 and not a physical one. Hence we are led to 

 conclude (in the words of Professor M. Foster), "That 

 an orange ray awakens either a simple sensory 

 impulse which developes into a complex sensation, or 

 a complex impulse (formed of impulses corresponding 

 to red and yellow) becoming converted into a mixed 

 or complex sensation." 



In this respect the eye differs strikingly from the 

 ear ; for two notes, when sounded together, do not 

 give rise to an intermediate note. The ear is able to 

 analyse such complex sounds more or less. 



The facts gathered from the above experiments 

 with the colour-top, are included in a more general 

 statement in regard to colour mixture which Max- 

 well proved to be true ; namely, that by combining 

 white or black with any other three colours, which 

 were sufficiently dissimilar, any other colour could 

 be matched. To assist in the comparison a smaller 

 disc of the colour to be matched is set on the face of 



FLOSCULARIA ANNULATA. 



ALTHOUGH this flosculehas not been described, 

 it was found (for the first time) in the summer 

 of 1882, in a marsh pool on Tent's Muir, Fifeshire ; 

 but only two individuals were found at that time. I 

 sent both of them to Dr. Hudson, of Clifton. One of 

 them died on the long journey ; the other survived, 

 but, unfortunately, arrived in a sickly condition. It 

 exhibited itself often enough, however, to enable Dr. 

 Hudson to draw a very good sketch of it ; but it was 

 in so laneuishine: a condition that it died before he 

 could make a satisfactory diagnosis of it. In the 

 summer of 1886, I found a few more specimens in the 

 Black Loch, Perthshire, and this summer (1887) I 

 have again fished a number of specimens out of the 

 same loch ; and these have afforded me ample 

 opportunity for studying the creature's habits. 



Its corona is a hemispherical cup, whose edge is 

 cut into three lobes of unequal size, the lobe on the 

 dorsal side being the largest. It differs from F. 

 trilobata and F. Hoodii (whose coronne also bear three 

 lobes), not only in the form of the lobes, but in th e 



