Ai'Kll., 191. 



KNOWLEDGE. 



157 



adjustments, and the liability to damage of the adjustment 

 itself must not be overlooked. 



The position of the milled heads should be such as to permit 

 of the hand or arm resting on the table while using them. 



Above all. particular attention must be paid to the sweetness 

 and ste.idiiu-ss with which the adjustment works, and the 

 following faults should on no account occur in use : Backlash, 

 loss of time or sag on reversal of movement, lateral movement 

 of the object across the field. And there should be no 

 tendency for an object to go out of focus if the table receives 

 a slight jar. 



These are all guarded against by well-fitting slides and the 



provision of suitable springs to keep the mechanism up to its 



work. Good working properties are ensured in different ways 



by different makers and it will be well in this connection to 



compare the advantages claimed for sprung and ground-in 



slides. If the adjustment slides of various microscopes are 



examined, some will be found to be " sprung " or slotted and 



held up true with screws, while others are not. Reliance, in 



the second case, is placed on the fit produced by grinding one 



part into the other. In support of sprung slides it is urged 



that when play through wear becomes noticeable, it may be 



taken up by tightening the screws and without returning the 



microscope to the maker. But against this advantage must 



be placed the difficulty of so exactly adjusting the screws that 



the slide works truly throughout its entire length and not only 



at a greater or less number of points. The alternative method 



of grinding one bearing part accurately into the other is now 



generally acknowledged as the better, but it involves the 



expenditure of much time in making a good fit and the use 



of very good materials if it is to wear well. Play is generally 



less than that in sprung slides, but when it does occur the 



microscope must be sent to the maker for readjustment. A 



good fitting should last for many years without any undue 



evidence of shake. ,, , ,, i. c- i- i /- 



H. Li.oYD Hind, B.Sc, P.I.C. 



QUEKETT MICROSCOPICAL CL LB. —February 27th, 

 Annual General Meeting. The Presidential Address was 

 delivered by Professor E. A. Minchin, M.A., F.R.S., who took 

 as his subject " Some speculations with regard to the simplest 

 forms of life and their origin on the earth." The most 

 distinctive property of living things is the power of metabolism. 

 All living bodies consist essentially of protoplasm which is 

 composed mainly of proteins. In all li\ing organisms certain 

 granules of a peculiar substance, chromatin, are found in the 

 cytoplasm. Chromatin consists of protein substances more 

 complex even than those found in the cytoplasm. The 

 simplest forms of life appear to be little or nothing more than 

 minute grains of chromatin. There are two views with regard 

 to the nature and composition of the body in the simplest and 

 most primitive forms of life; the first, the chromatinic theory, 

 assumes that the primitive living substance is chromatin, and 

 that the earliest forms of life were minute particles of 

 chromatin ; the second, the cytoplasmic theory, regards the 

 cytoplasm as the primitive living substance, and supposes that 

 the earliest living things were composed of cytoplasm alone. 

 .As an example of theories which maintiiin that life originated 

 on the earth, that of Sir Ray Lankester was mentioned, 

 according to which it is supposed that life originated at the 

 time when the earth had cooled down suflficiently to have 

 a firm crust upon which water was condensed. The 

 chemical and electrical disturbances which undoubtedly 

 then occurred might conceivably have brought about 

 synthesis of organic compounds in a manner and to an 

 extent which does not occur at the present day. This synthesis 

 might conceivably have culminated in proteins and the pro- 

 duction of the earliest protoplasm, and the earliest living things 

 would probably have been relatively large masses of cytoplasm, 

 in which chromatin was a product formed later. As an 

 example of theories which assume that life was in some way 

 brought to the earth when it was cooled sufficiently for life to 

 exist upon it, that of Professor .Arrhenius was taken. He 

 regards life as eternal and cpeval with our universe, and 

 believes that it exists throughout the universe in the form of 

 minute particles (,? chromatin), which are transported through 

 infinite space by radiation pressure. A particle in size of the 



order of 0-16m would be required, and it is probable that 

 some of the almost invisible microbes of certain diseases 

 (Chlamydozoa) are of smaller dimensions than this value. It 

 is not possible to decide in favour of the one theory or the 

 other in the present state of our knowledge of living things. 



ORNITHOLOGY. 



By Hugh Boyd Watt, M.B.O.U. 



CASUAL BIRDS IN THE BRITISH ISLES. — Birds 

 as a class are great vagrants, and the avi-fauna of the British 

 Isles is steadily being augmented by new species, such as 

 those which have been reported in recent numbers of 

 " Kn'owlkdge." These, with other very rare occasional 

 and accidental visitors, may be called natural "' casuals." It 

 is difficult to draw a line between rarity in the occurrence of 

 a species and casualness, for it is not adequate to say that, 

 in the last-named, what is called " chance " must be present. 

 Under quite natural conditions it seems to be the same factor 

 of chance which shapes the destiny of those bird-waifs, many 

 different kinds of which have now occurred in the British 

 Isles, often blown or strayed out of their course on migration. 

 In illustration of the large casual or occasional element 

 amongst British birds it may be said that, of the four 

 hundred and fifty species or thereabouts now admitted to our 

 list, no fewer than two hundred and seven are classed as 

 occasional visitors and not breeding. These cannot all or 

 always be correctly called casuals, but a large number of them 

 have the most slender claims to be called British. Of the two 

 hundred and seven, some one hundred and five have not 

 occurred more than six times each, and some of these only 

 once or twice. 



.\ much less questionable casual element is composed 

 of foreign species, mostly introduced by man, and taking to 

 freedom for a time or tentatively. This excludes such birds 

 as the Pheasant and Red-legged Partridge which have been 

 long naturalized in this country. .Accidental or temporary intro- 

 ductions are a different thing, and the following incident is 

 suggestive of what may have often happened, although 

 perhaps not in quite the same way. When the steamer 

 ■' Minnehaha" was wrecked on the Scilly Isles, in April, I'JIO, 

 a number of .American birds on board, consigned from New York 

 to the Zoological Gardens, London, were liberated to give them 

 a chance to save themselves. -Amongst them were Parrotlets, 

 Ground Doves, Inca Doves, Crested Ouails, Red-winged 

 Starlings and Purple and Bronze Grackles,which,if finding their 

 way ashore, would make a strong casual element for, at any rate, 

 a brief time in the avi-fauna of the place. Ships, unwittingly, and 

 sailors and travellers purposely, often bring foreign animals of 

 different kinds to our country, birds probably most abundantly. 

 When the steamer "Mauretania" was about five hundred 

 miles out from New York, eastward bound, on 15th June, 1911, 

 a Curlew came on board and remained for three days, leaving 

 only when the Irish Coast was sighted (Coward's " .Migration 

 of Birds." 1912. Page 122). No doubt it made the land 

 and thus joined the bird population of the British Isles. Even 

 native species are sometimes so conveyed, as the case of the 

 Peregrine Falcon given in the last issue of " Knovvlkdge " 

 (page 116) shows. 



The spire of Shoreditch Church was the home of a 

 solitary Falcon for many years, and Kites which were 

 liberated from the Zoological Gardens, London used to 

 return there to feed. .A Black Kite, which had escaped 

 from its cage there, would fly over the heads of visitors 

 quite unconcerned, in the hope of having tit-bits thrown 

 to it. The sight of this raptorial bird on the wing caused so 

 great a panic amongst the smaller birds in the aviaries that 

 after a week's freedom it was induced to return to 

 its cage. A still larger bird of prey which has accidentally 

 been at large in London is the Vulture. In August, 

 1898, five Jamaican Vultures were free in the Borough, haunt- 

 ing the house-tops and steeples for some days; and in the same 

 month one, which was consigned to the Hungarian Exhibition, 

 Earl's Court, escaped from a broken crate and took to such 

 freedom as the neighbouring roofs afforded. 



