Dublin Microscopical Club. 145 



delicacy which characterizes that instrument, this one was made 

 rather roughly and strongly, rendering it more suitable for ordinary 

 use. In place of a costly knife, of peculiar pattern, it worked witlx 

 an ordinary razor, and was adapted for freezing tissues by means of 

 ether. By a simple arrangement which Dr. Scott fitted to it, con- 

 tinuous series of sections of known thickness could be cut with ease. 

 The price was also exceptionally low. 



Chert with Sponge-spicules. — Prof. Sollas showed sections of chert 

 from Lias with sponge- spicules. 



Experime-fits to illustrate the Application of the Microscope to 

 practical Mineralogical Questions, were shown by Prof. Tichborne, 

 In examining an argentiferous mineral which was found in Wales, 

 and known there as " blue stone," it became desirable to determine 

 whether the said mineral was a definite double sulphide of lead and 

 zinc, or whether it was a fine mechanical mixture of the two well- 

 known minerals galena and blende. The said blue stone had been also 

 found in Ireland at Ovoca, and being considered a definite mineral, 

 had been christened Killmacooite, from a local name. Dr. Tichborne 

 found that on gradually powdering the mineral and examining it 

 from time to time under the microscope, a point was at length reached 

 when half the particles became transparent and transmitted light, 

 whilst no amount of powdering would render the other particles 

 transparent. To try such an experiment it was necessary to view 

 with very strong transmitted light (a half-inch object-glass) and 

 to cut off all reflected light. From this experiment he came to the 

 conclusion that the mineral was an intimate mixture of fine crystals 

 of blende and galena, the blende being the transparent particles and 

 the galena the opaque. Although both these minerals possess a certain 

 degree of metallic lustre, galena is one of the most perfectly opaquo 

 substances known, whilst blende in very thin layers is perfectly 

 transparent. Prof. Tichborne illustrated this by depositing thin 

 layers of artificial galena and blende upon glass by the action of 

 sulpho-urea upon alkaline solutions of the respective oxides of lead 

 and zinc. 



October 16, 1884. 



Structure of Leaves of Abies subalpina, Engelm. — Prof. M'Nab ex- 

 hibited sections of leaves of Abies subalpina, Engelmann, which he 

 had collected in Kicking Horse Pass, Rocky Mountains, Sept. 12, 

 1884. These differed in no way from leaves of the type specimen 

 of Abies lasiocarpa, Hooker, a species sent by Douglas from the 

 very same region, and thus, according to the strict law of priority, 

 Engelmann's recent name should be rejected. 



Zygospore of Cosmarium cucurbita. — Mr. Archer showed the zygo- 

 spore, or Avhat appeared to bo the zygospore, of Cosmarium cucur- 

 bita, collected by Mr. Pim at Killarney a few weeks previously. 

 This formed a somewhat elongate, on the whole subeJliptic figure, 



