274 



HARBWICKE'S SCIENCE-GOSSIF, 



having been drifted some distance away from their 

 original place of growth, no specimens of tliis tribe 

 have been found iti situ, or on the very spot where 

 they grew, that I am aware of, such as is very fre- 

 quently tlie case with Sigillaria and other coal plants. 

 The fossil pines are nearly always decorticated, being 

 devoid of leaves, branches and bark, and occur in a 

 fragmentary condition. Those which show structure 

 are found in calcareous nodules, which also contain 

 marine shells and fish remains, but there can be no 

 doubt of the fact that these plants are land plants, 

 and must have come from some neiglibouring land, 

 and many of them have probably been carried a 

 long way from their native soil, down the ancient car- 

 boniferous rivers before reaching their final resting- 

 place in the sea. The larger tree-like forms became im- 

 bedded in the sandbanks at the mouths of the rivers, 

 while the smaller branches and stems were carried 

 farther out to sea, and ultimately sank to the bottom 

 and became imbedded in the limy ooze and enclosed 

 in nodules along with the remains of the shells and 

 fishes inhabiting that sea. It is also worthy of note, 

 that the Dadoxylon has not been found in our coal- 

 balls, which shows that they preferred a different 

 locality to that in which the Calamites and Lepido- 

 dendrons flourished. The small fruit stones which 

 occur so plentifully in some sandstone rocks called 

 Cardiocarpons and Trigonocarpons are supposed to 

 have belonged to Dadoxylon. Our coal-balls yield a 

 great variety of these fruits, but these very probably 

 belong to another fossil pine which was associated 

 with the Lepidodendroid plants, and which I shall 

 ■describe in my next paper. 

 Halifax. 



LIST OF ASSISTING NATURALISTS. 



[Continued.'^ 



Essex .\nd Middlesex. 



London. Thomas S. Morten, 42 Haverstock Hill, 

 N.W. Fhaiierogamic Botany, Exogcns, Emiogens, 

 and Micro-Fungi. 



Middlesex. 



Ealing. George D. Brown, Henley Villa, W. Sub- 

 jects : Cryptogamic Botany, especially Diatoinacac 

 and Micro-Fungi ; Folyzoa, British and foreign, 

 recent and fossil. 



Yorkshire. 



Sheffield. J. W. Williams, Wesley College. Zoology, 

 Lfpidoplcra, and Taxidcniiy. Correspondents please 

 enclose stamped addressed envelope. 



Erratum. — Science-Gossip, October ist, 1881 ; 

 page 221. For " E.itinct Volcano, Isle of Mull," read 

 •" Lava Stream or Dyke, Carsaig or Charsaig Bay." 



MICROSCOPY. 



A Hollow Glass Sphere as a Condenser 

 FOR Microscopic Illumination.— A glass globe 

 filled with water has long been employed by watch- 

 makers and engravers for the purpose of condensing 

 the light upon their work ; it was also used by some of 

 the early microscopists. Ledermiiller, in his " Mikro- 

 skopische Gemiiths- und Augen-Ergozung " (Micro- 

 scopic Mind-and-eye-delights) 1763, gives a repre- 

 sentation of his lamp and condenser : the latter is a 

 globe without foot or neck, and is supported on the 

 top of a square brass rod by six claws, the lamp 

 being supported in a similar manner, both of them 

 sUding into square holes at the opposite ends of a 

 brass arm fixed on a stand. In the " Micrographia," 

 Hooke gives a figure of his microscope and acces- 

 sories, amongst them is a globe condensing the light 

 on the stage of the instrument. This form of con- 

 denser was probably used by many of the old 

 microscopists, but it appears soon to have fallen into 

 disuse, as it is not mentioned by Adams in his 

 " Micrographia Illustrata," 1771, or in his "Essays 

 on the Microscope," 1787. Possibly the opticians 

 of the period did not care to introduce so simple 

 and inexpensive a contrivance to their patrons (mine 

 cost one and eightpence). I had looked upon the 

 " globe condenser" as one of the relics of the past, 

 and not worthy of resuscitation ; until a short time 

 ago when watching an artist engraving some fine 

 shading on wood, I was struck with the sharpness 

 and definition of the engraved lines (about Jg inch 

 apart). It at once occurred to me that this kind of 

 illumination would suit the microscope. I therefore 

 borrowed it and tried it first with a \ objective (a 

 Ross 75°) upon Plenrosignia aiigiilaliiiii, using oblique 

 light from the mirror ; the stria; came out very dis- 

 tinctly. I then removed the globe, and the stria 

 vanished and required a more oblique ray to render 

 them again visible. I next tried it onSynedra robusta 

 and resolved the strict into beads; this I had not 

 been able to do before with this objective. I next 

 tried it with low powers (liin., i in., and § objec- 

 tives). I first used the 5, but forgot to alter the 

 previous position of the mirror, and consequently 

 obtained a "black field," the object I had placed 

 upon the stage was Halioiiuiia llutnboldtii. I was 

 surprised at the beautiful effect upon that form. It 

 appeared as though illuminated by intense moonlight 

 with a slight green tinge and delightfully cool to the 

 eye. I have since purchased a smaller globe (6 inches 

 in diameter) than the one I tried; the liquid with 

 which it is filled is a dilute solution of sulphate of 

 copper (about \ ounce of saturated solution to i pint 

 of water). The mixture must be filtered if ordinary 

 water is used ; the intensity of colour is however 

 somewhat a mailer of taste. The distance of the 

 lobe from the lamp should be about two or three 



