438 



KNOWLEDGE. 



NOVEMUKR, 1912. 



" (3) The lid could not be lifted off at .iny time for the contents 

 to be examined, and considerable trouble had to be spent in 

 imscrcwing it in order to clean out the boxes at the end of the 

 season. 



" (4) The inside, which was cut out very carefully to imitate 

 the hole bored by a Woodpecker, did not provide much room 

 in the smaller-sized boxes for large broods, and all the trouble 

 was thrown away in the case of all those which were fastened 

 low down on the trees for the smaller birds. I therefore spent 

 some amount of time and trouble, with the help of a member 

 who has a joinery works, in producing a kind of box suited to our 

 re(|uirements, and these have been very successful. We made 

 very rigorous tests last year with which we werc<niite satisfied. 

 " We find, also, that the opening of the box at the top (insttad 

 of at the fronti does not disturb the birds if they happen to 

 be sitting. A great deai more pleasure is, therefore, given to 

 those who put up the boxes. The eggs and young can also be 

 seen more easily, and tiuite useful nature study observations 

 can be made, in which case even the commonest birds arc useful. 

 "We have not forgotten that birds like the Woodpecker and 

 the Wryneck make no nest and if their eggs are to be kept 

 together for hatching a flat-bottomed box is useless. The 

 bottoms of all the boxes are slightly curved, but special cup- 

 shaped bases are put into those which are fastened high in the 

 trees. We make specially large openings for Robins and 

 restrict the size where only birds useful to the gardener are to 

 be encouraged. It is useful to bear in mind that the Common 

 Sparrow and Starling seldom build low down. 



" I might call attention to the fact that a small series of boxes 

 is on view in the Zoological collection arranged at this meeting 

 of the British Association by Section D (Zoology). 



" In addition to the birds that nest, we have a number that 

 always seem to be present, but whose eggs we have not found. 

 The list includes three species of Woodpecker, and the Brown 

 Owl, which up to the present has refused all the nesting sites 

 put up for its benefit. The Barn Owl is often to be seen, as 

 is the Golden-Crested Wren. The Nightjar has been present 

 during three seasons, the Kingfisher is a common visitor, and 

 Jays and Magpies occasionally appear. 



" Snipe sometimes frequent the outskirts of the wood and, on 

 one occasion, I found a dead Woodcock within its boundary. 

 This bird my wife had apparently seen alive a few days pre- 

 viously. Recent records include the breeding of the Goldfinch, 

 Redpoll, Marsh Tit and the Wryneck. 



" It will be noted, however, that very few of these birds are 

 really rare ; but it is the object of the Connnittee to protect 

 those which occur near London. In the Brent Valley, there 

 are few crops grown that the birds are likely to damage ; but 

 in other localities it might have to be borne in mind, when 

 doing similar work, that certain species should not be unduly 

 encouraged or indeed given protection. 



'■ It is practically impossible to describe all the pleasure that 

 can be obtained from such a reserve. It is a source of 

 interest all the year round, and the mammals, reptiles, insects, 

 and other creatures should be taken into consideration. The 

 mice are somewhat destructive to eggs, but the way in which 

 they utilise old birds' nests is worthy of attention. The 

 fungi may be mentioned and a bird reserve also becomes a 

 sanctuary for flowering plants. Steps will be taken to form 

 committees in other parts of the country, and I should be 

 very pleased indeed to give any advice that I can to those 

 who are thinking of protecting any definite areas in the way 

 which has been outlined." 



"BRITISH BIRDS." — The October number of this 

 Magazine contams, as usual, many interesting notes. Miss 

 Turner contributes an article and photographs on the 

 Bearded Tit. while the Rev. F. C. R. Jourdain discusses the 

 known cases of hybrids between Black Game and the 

 Pheasant. A clutch of white eggs of the Ringed Plover is 

 recorded for Blakeney Point in Norfolk, and we have 

 accounts of the attempted breeding of the Grey Wagtail in 

 Surrey, as well as the probable nesting of the Pied F'ly- 

 catcher in Moray. Another matter of interest is the case of 

 a Stock Dove laying again, as the Common Pigeon sometimes 

 does, while its young were still in the nest. 



By liUGAK Sk.mok. 



EXPOSURE TABLE FOR NOVEMBER.— The calcula- 

 tions are made with the actinograph for plates of speed 200 H. 

 and D., the subject a near one, and the lens aperture K.16. 



Remarks. — If the subject be a general open landscape, take half 

 the exposures given here. 



PHOTOMICROGRAPHY OF OPAOLE OBJECTS.— 

 Of late, considerable attention has been given to studying the 

 microscopical structure of metals and alloys (mctallographyl, 

 and in this work photography plays a very important part. 

 The specimens, which may be either fractured surfaces or 

 polished ones etched with some material suitable to show the 

 desired structure, may, " if small," be held in position on a 

 glass slip by means of plasticine. In any case, the objects, 

 being opaque, require to be illuminated by means of reflected 

 light. When using low powers, diffused daylight is probably 

 the best to employ, as an even illumination without deep 

 shadows should generally be aimed at. In this case a vertical 

 camera is a great advantage, as good lighting can be more 

 readily obtained by its use. When employing daylight the 

 camera should be placed near a fair-sized window, in such 

 a position that the light falls upon the object from above as 

 well as from the side. With a little care and attention to 

 details it will be found fairly easy to obtain good results in 

 this way. This method, however, is only suitable for very 

 low magnifications, and even then unless the light is very 

 good the exposure is unduly prolonged. 



For many objects a condenser may be employed but care 

 must be taken to avoid too much glare. When using artificial 

 light such as an oil lamp, the bulls-eye condenser will be found 

 useful, and this, when used in conjunction with a parabolic 

 reflector will be found to illuminate opaque objects beauti- 

 fully. Methods of this kind, however, can only be made use of 

 with low powers such as twenty-four millimetre or sixteen 

 millimetre objectives, as with lenses of a shorter focus than 

 this, the working distance is too close for the light to reach 

 the object. In this case some form of vertical illuminator, an 

 appliance for passing the light through the objective becomes 

 necessary. In its simplest form this consists of a thin 

 circular disc of glass contained in a short mount which is 

 attached to the lower end of microscope and into which the 

 objective is screwed. A be;im of light directed upon an 

 aperture in the side of the mount by means of a bulls-eye, 

 falls upon the reflector, and is projected downwards through 

 the objective, and thus illuminates the object. This illumina- 

 tor being transparent allows the light reflected from the 

 specimen to pass through it, and reach the eyepiece, by 

 which the image is viewed, in the ordinary manner. Care 

 has to be taken in the adjustments of the apparatus, in order 

 to avoid any veil or mistiness being imparted to the image 

 under observation. 



Instead of the disc of glass a small prism may be used, 

 when a beam of light directed upon the opening in the side of 

 the mount falls upon the prism, and becomes totally reflected 

 from the hypotenuse surface downwards through the half of 

 objective which it covers, and reaching the object brilliantly 

 illuminates it. Thus the image seen through the eyepiece is 

 entirely produced by the uncovered half of objective. For 

 either method of lighting, the object should be uncovered or 

 in optical contact with the cover glass, and objectives of higher 



