27 



has not boon decorated -with coloui', until on entering the choir 

 the well-known dark wooden carving- is seen. This effect is 

 most probably due to reflected rays of light suffering interference 

 on passing through thin films, caused by age upon the glass, 

 and only waves of light of a certain length reaching the eye the 

 effect of colour is i)roduced. It must not bo be confounded 

 with the reflection of the stained glass windows or the beautiful 

 tints they throw on the columns when the sun shines through 

 them. It is so cimous that it is remarkable it has not attracted 

 more attention.* — Some diagrams were then shown illustrative 

 of the refraction of light in passing through a medium, 

 gradually decreasing in density, and triangular prisms. Also 

 the iuterforenco of waves of liglit producing colour, on being 

 reflected from, or in transmission and reflection through thin 

 transparent films. 



MARCH. 



0)1 the Ascidian, hy Colonel Horslerj. 



Colonel Horsley, E.E., exhibited a dwarf specimen of an 

 Ascidian, which has existed in his salt water aquarium for up- 

 wards of eighteen mouths and seems quite reconciled to its con- 

 finement. It belongs to the class of Tunicata, which includes the 

 lowest of the Acephalous MoUusca, which are destitute of the 

 power of forming a shell, but which have the outside of the man- 

 tle condensed into a tough, leathery, or cartilaginous tunic, from 

 which their name is derived. Many of them live separatelj'-, and 

 have the power of freely moving through tlie water. Others 

 associate together into a compound mass ; of which, however, the 

 individuals are not connected by any internal union. But others 

 form really compound structures, each individual being able to 

 live by itself alone ; but being connected by a stem and vessels 

 with the rest. The general structure of the individuals is the 

 same, however, in the single and in the composite animals of 

 this class. The cavity of the muntlu possesses two orifices ; by one 

 of wliicli a current of water is continually entering, whilst by the 

 other it is as continually flowing out. These oiifices lead into a 

 large cliambcr, the lining of which, folded in various ways, 

 constitutes the gills ; and at the bottom of this chamber lie tlie 

 stomach, and the intestinal canal, which terminates near the 

 aperture for the exit of the water. All these parts are covered 

 with cilia, by the action of which a continual stream is made 

 to flow over the gills, and to enter the stomach ; and 

 the minute particles, which the water brings with it, and 



* Note. — ThispUstiomenou is uo 1 iDger observaljlo, as tie Cathedral is now 

 lighted by rowa of gas juts instead of standards. 



