[96] There is a much more scientific mode of trying this experiment. A description of the instrument (Kaleidophone), and cuts of the figures produced, may be seen in Tyndall on Sound, pp. 132. seq. [97] There is reason for believing that a large proportion of animal eyes see much as ours do when in a normal state. Colour blindness is frequent in Man and occurs between red and green, yet a bull distinguishes the two like a _healthy_, human being. He is allured by the sight of a green field, and lashes himself into fury when a red rag is waved before him. The eyes of insects are very far removed in structure from ours. A butterfly's compound eye contains 17,000 tubes, that of the Mordella beetle 25,000. Their perception of colours appears vivid and distinct. They resemble birds, reptiles, and other creatures in choosing for their lairs and resting-places objects _coloured like themselves_. It is not difficult to mount one of these compound eyes, so as to look through it by aid of a lens placed in focus. Leeuwenhoeck looked through the eye of a dragon fly (made up of 12,544 tubes), "and viewed the steeple of a church which was 299 feet high, and 750 feet from the place where he stood. He could plainly see the steeple, though not apparently larger than the point of a fine needle. He also viewed a house in the same manner, and could discern the front, distinguish the doors and windows, and perceive whether they were open or shut." See _Insect Miscellanies_, p. 129. [98] Two points connected with colour admit of being easily experimented on, and deserve from their interest to be made the subjects of repeated observations. The first has relation to the question of _primary_ colours;--are they alike in man and in _all_ the lower animals?--In birds and reptiles there are anatomical reasons for believing the primaries to be red, yellow, and blue. But are they the same in our race?--may they not more probably be red, green, and violet? In this case yellow is the transition from red to green, blue from green to violet. As colour blindness consists in an insensibility to red, and as the outer circle of the field of vision is feeble in its reds, the number of experiments which might be suggested is evidently considerable.