Febkuary 1, 1897.] 



KNOWLEDGE, 



51 



savant, M. Renault, was examining thin sections of coal 

 under the microscope, and noticed certain clear bands in 

 the dark substance of the coal. On looking closer he 

 found that these were made up of minute bodies in the 

 characteristic groups and clusters of micrococci and bacilli. 

 Thus we find that the bacillus, which has only been known 

 to science for some two hundred years, has in reality 

 existed as far back as the carboniferous epoch. This is 

 interesting in itself, and raises the further question whether 

 bacterial action may not have been an agent in the for- 

 mation of coal. In favour of this view we have the fact 

 that the number of bacteria in coal exceeds that in vege- 

 tation preserved by silica or carbonate of lime, and that 

 the species are fewer. Also that they are not coloured 

 like the coal, but appear as clear bands. On the other 

 hand, we know that the general result of bacterial action 

 is the complete destruction of vegetable fibre. If, then, 

 the bacillus has been an agent in the formation of coal, 

 we must suppose the action to have been arrested at 

 dififerent stages for the difterent sorts of coal. 



Oorbridge-on-Tyne. G. W. Buljian. 



STAR STSTEMS. 

 To tJie Editors of Knowledge. 



Sirs, — It is not easy to follow Mr. Monck's argument in 

 his letter, page 27.5. I take it that he is seeking to throw 

 light on the discussion, in your October and November 

 Numbers, as to the correctness of the late R. A. Proctor's 

 theory that most of the bright stars in Charles's Wain form 

 not only an apparent group but a real one, and that they 

 are drifting together through space. As Mr. Monck 

 himself points out, the case of stars in widely separated 

 portions of the sky is a totally different one, and throws 

 no light on the question ; so it does not appear why he 

 refers to such cases. The question is, Is the proper 

 motion of the stars under consideration in sufficient 

 agreement, and is their parallax sufficiently imperfectly 

 known, to afford a probability that they are travelling 

 together ? -Judging bv the drawing on page 251, must we 

 not answer the first part of the question in the affirmative — 

 at least as regards -/, S, ;, and ? ? Perhaps Mr. Monck can 

 answer as to the second point. We must bear in mind, 

 too, that while common drift gives some presumption in 

 favour of a connected system, motions in different 

 directions are no proof of the absence of such connection — 

 at least, unless continued for a long period; for it is quite 

 possible that a star may be revolving in a wide orbit round 

 a dark star, in which case one needs to know the proper 

 motion of the centre of gravity of the pair. 



Sunderland, T. W. Backhouse. 



.January 18th, 1897. 



-*i»« 



THE LEAP-CCXTER BEE. 

 To the Editors of Knowledge. 



Sirs, — I have read with considerable amusement Mr. 

 Fred. Knock's letter, in which he endeavours to prove that 

 my article on the leaf-cutting bee is inaccurate. Mr. 

 Enock's corrections, however, are unfortunately distinctly 

 incorrect, as I am able to testify, both from personal 

 observation and the authority of such weU-known scientific 

 men as Prof. W. S. Dallas, F.L.S.; Prof. F. V. Theobald, 

 M.A., F.E.S. ; and my father, the late Prof. P. M. Duncan, 

 F.R.S., F.L.S. 



Mr. Enock's first statement — " As soon as the leaf- 

 cutter bee has made her burrow, she flies off" and selects a 

 rose-bush of the ' tea ' type ' — is most misleading, as it gives 

 the reader the idea that the bee confines herself solely to 

 this species of rose-bush for the material with whicTi she 



forms her cells. I have proved by personal observation 

 that these bees do not confine themselves to one species 

 of rose-bush. Prof. W. S. Dallas states : " The rose, 

 laburnum, and garden acacia seem to be the favourite 

 trees with these insects " ; and again. Prof. F. Y. Theobald 

 says the bees " line the tunnels with pieces of rose and 

 otlh'r leaves."' 



Mr. Enock then goes on to say the bee " first cuts a 

 circular piece somewhat larger than the diameter of the 

 burrow, into which she fits it at the bottom. " This is 

 incorrect. The first piece of leaf used is oblong and 

 narrower at one end, and this narrow end is folded under 

 to form the base of the cell ; the succeeding six or seven 

 pieces being similar in shape, varying slightly in size. I 

 have carefully examined several cells (some of which I 

 have in my possession at the present time), and have never 

 found as many as twelve of these oblong leaves, the usual 

 number being seven or eight. 



I cannot imagine on what authority Mr. Enock asserts 

 that '• as many as a dozen circular pieces " are used to 

 close the mouth of the first cell, when it is an acknowledged 

 fact that the maximum number of circular pieces is four, 

 but usually only three are found. These circular pieces do 

 not form the foundation of the next cell, each ceU being 

 complete in itself. 



The bee-bread, which Mr. Enock describes as a "delicious 

 pudding," is actually a dark, compact mass, emitting a 

 fcetid odour. 



Francis M. Duncan. 



3, Chesterton ViUas, Warwick Road, RedhUl. 

 January 12th, 1897. 



THE ZODIACAL LIGHT. 

 By Lieut.-Col. E. E. Mark\«ck, F.R.A.S. 



THE season when this phenomenon is visible after 

 sunset is now approaching, and it may be in- 

 teresting to take stock of what we know about it, 

 which, after all, seems to be surprisingly little. 

 It is generally dismissed in the text-books with a 

 pretty short notice, and sometimes is not mentioned at aU. 

 Although it can hardly be called a popular object in the 

 sense that Mars or Jupiter is, still there must have been a 

 great number of observations made of it at different times, 

 and one looks for a corresponding definite advance in our 

 knowledge of its interior economy. But the conditions 

 of its visibUity in our latitude render exact observation 

 extremely diflicult. Like the inferior planets. Mercury 

 and Venus, it is seldom, if ever, seen more than three or 

 four hours after sunset or before sunrise, and cannot be 

 observed on the meridian. Again, its tenuous and ethereal 

 character render it a difficult matter to note definite 

 particulars of its shape, size, or position. In these 

 respects no instrument is of the slightest service ; but the 

 observer should be one with a keen eye, which can take in 

 a large area of the sky, and is quick in apprehending 

 differences in brightness of particular areas. No telescope 

 can do this, and, even with a binocular, the field of view 

 commanded is far too small. The best way is to sweep 

 the eye rapidly right and left, up and down — that won- 

 derful faculty of " averted vision " assisting to note very 

 faint degrees of light. 



My own experience, based on some sixteen years of 

 observation in different latitudes, is that provided one has 

 a clear country horizon remote from the glare of towns or 

 electric lights, with a dark clear sky in January or 

 February, there is no difficulty to the ordinary observer in 

 England in detecting, soon after sunset, the pearly cone 



