86 



HARDWICKE'S SCIENCE- GOSSIP. 



type, they may have been constructed for quite 

 different uses, and in some places at first it may not 

 be apparent what was the original object of the 

 erection. Eor if, for farming purposes, as is often 

 the case, all the stones of a cam or the clay of a 

 tuaim be removed, and only the kistvaen left, the 

 latter may easily be mistaken for a cromleac or true 

 altar, more especially if it is one of those types of 

 kistvaen that is open at both ends. These cromleac- 

 looking structures having been exhumed from cams 

 and tuaims of late years, has induced various wild 

 theories, and led some to believe that all structures 

 of the same or similar type are sepulchral or 

 monumental, although in' many cases it is quite 

 apparent they are only a small portion of a once 

 extensive erection, while in or near some of the 

 fosleacs no burial could have taken place on account 

 •of the surface of the ground being a solid rock. 



MICROSCOPY. 



Uniformity in Magnifying Standard.— In 

 the November number of Science-Gossip you 

 published a letter from Mr. Guimaraens on the im- 

 portance of uniformity of gauge for the so-called 

 universal screw. May I venture to call the atten- 

 tion of your readers to a uniformity in another de- 

 partment of microscopic work, more important and 

 less general than that other : I mean the uniformity 

 of standard of the magnifying power of objectives. 

 This subject has been already alluded to in the 

 December number of the Monthly Microscopical 

 Journal. Such uniformity, if practicable, would be 

 a boon, I think, not only to inexperienced beginners 

 when setting up their series of powers, but to all 

 who are engaged in microscopic work. There may 

 be difficulties, unknown to me, which render such 

 uniformity impracticable ; and there may be advan- 

 tages in diversity which make it inadvisable. As 

 an amateur, I do not consider myself qualified to 

 discuss the question; all I wish to do is to call 

 attention to the subject, and to express a hope that 

 the Microscopical Society may see its way to relieve 

 us from the present state of confusion and uncer- 

 tainty, which naturally result from the absence of 

 any uniform standard of magnifying power.— Z. 



Earth - dwelling AivkebyE. — The ubiquitous 

 nature of the lower organisms has been noticed in 

 previous volumes of Science-Gossip. Many species 

 of diatomaccae may be found on mosses growing on 

 truuks of trees or on old thatch; rotifers in the 

 dust accumulated in lead gutters and cisterns ; and 

 Professor Leidy* says that, instigated by the re- 

 searches of Professor E,. Greet', of Marburg, pub- 

 lished in Schultze's " Archiv f. Microscopische 



* Silliman's American Journal, January, I875. 



Anatomie," ou amoebae living in the earth (iiber 

 eiuige in der Erde lebende Amoeben), induced him 

 to look for Rhizopods in similar habitats. In the 

 earth, or about the roots of mosses growing iu the 

 crevices of the bricks of our city (Philadelphia) 

 pavements, in damp places, besides finding several 

 species of Amoeba, together with abundance of the 

 common wheel animalcule, Rotifer vulgaris, I had 

 the good fortune to discover a species of Gromia. 

 I say good fortune, for it is with the utmost pleasure 

 I have watched this curious creature for hours to- 

 gether. The genus was discovered and well de- 

 scribed by Dujardin from two species, one of which 

 (G. oviformis) was found in the seas of France, the 

 other (Gr.jlaviatilis) in the river Seine. Imagine 

 an animal like one of our autumnal spiders stationed 

 at the centre of its well-spread net ; imagine every 

 thread of this net to be a living extension of this 

 animal, elongating, branching, and becoming con- 

 fluent, so as to form a most intricate net; and 

 imagine every thread to exhibit actively moving- 

 currents of a viscid liquid both outward and inward, 

 carrying along particles of food and dirt, — and you 

 have some idea of the general character of a Gromia. 

 The Gromia of our pavements is a spherical, cream- 

 coloured body about T Vth of a line in diameter. 

 When detached from its position and placed in 

 water, in a few moments it projects in all directions 

 a wonderful and intricate net. Along this net float 

 minute navicula from the neighbourhood, like boats 

 in the current of a stream, until, reaching the 

 central mass, they are swallowed. Particles of dirt 

 are also collected from all directions and accumu. 

 lated around the animal, and when the accumulation 

 is sufficient to protect it, the web is withdrawn, and 

 nothing apparently will again induce the animal 

 to produce it. Gromia terricola, as the discoverer 

 proposes to name this organism, covers an area of 

 nearly half a line in diameter. The threads of the 

 net are less than 3-^0 oth of an inch in diameter. 



Air-bubbles. — The easiest method of getting rid 

 of air from zoophytes that I have met with is boil, 

 ing them in methylated alcohol in a test-tube. This 

 will free most zoophytes, or, iu fact, any cellular 

 substance, such as wood-sections, hair, &c, from 

 bubbles, and the objects may be afterwards mounted 

 in glycerine jelly. — C. C. Underwood, 



Mounting in Balsam. — The late Professor 

 Walker-Arnott never to my knowledge boiled the 

 balsam. His practice was to hold the glass slide 

 sufficiently long over the spirit-lamp to evaporate 

 the turpentine before placing on the cover. The 

 evaporation would generally be effected in thirty or 

 forty seconds, if held at the distance of 3 or 4 in. 

 from thcllamc ; and although he afterwards finished 

 off his mountings with an asphalt ring, the balsam 

 was always hard enough immediately on cooling to 

 admit of being scraped away from the edges. My 



