JCLY 21, 1882.] 



♦ KNOWLEDGE ♦ 



127 



It will seldom be found that a tree, a figure, or other 

 prominent object, is placed centrally. But there are ex- 

 ceptions to this ruh', which need act be considered here. 



The use of the quick gelatine plates makes it possible to 

 introduce cattle into the foregrounds of photographs, and 

 these, if fortunately placed, make a most valuable adjunct, 

 and considerably enhance the artistic value of the result. 



For distant views, wide - angle lenses sliould not be 

 used ; the eftect is to dwarf distant objects. The natural 

 angle of vision is about GO degrees ; therefore, if much more 

 of the subject be included, it cannot have an appearance 

 true to nature. Such lenses are valuable for near views, 

 as they enable us to bring into the picture points wliich 

 assist to make it more complete ; and the defect visible 

 in distant views taken with such a lens is not apparent in 

 the near view. 



The beautiful atmospheric eflFects often seen in nature 

 when there is a slight haze over the distant landscape, 

 from an artistic point of view, is one of the most charming 

 aspects of nature ; but, unfortunately, is not always suitable 

 for photography. Tlie distant hills just visible through 

 the haze may not be visible in the photogi-aph, and we 

 have only the foreground and mid-distance. On the other 

 hand, the ert'eet in a photograph is not good wlien the 

 distance is as clearly defined as the foreground. Unfor- 

 tunately, the amateur cannot always choose his light or 

 time of day for taking his views. He is possibly merely 

 passing through the scenery, and he must take just what 

 he happens to see at the time : therefore, it must very 

 frequently happen that a good picture comes by chance, 

 and the majority of photographs are only of interest as 

 records of what happened to be the eflect at the instant 

 the view was taken. 



The charming photographs one sees occasionally are 

 usually the result of much patient waiting. It often occurs 

 that the best view of a place can only be obtained at a 

 certain time of the day, and to obtain that view it may be 

 necessary to wait u.any days so as to catch nature just at 

 the favourable moment — the result may be worth all the 

 waiting. 



In photographing buildings (or any other object indeed) 

 care should be taken that the camera be level. This can 

 be done with suflicient accuracy by the eye, and to avoid 

 too much'foreground the lens may be lifted by the sliding 

 front. When the camera is provided with a swing back, 

 the defect arising from having to raise or depress the 

 camera may be obviated. ' " ' 



In taking views it not unfrequeiitly happens that the 

 sun may be shining directly into the lens. Sucli being the 

 case, the greatest care must be taken to shield the lens in 

 some way, or the plate will certainly be fogged. 



The most usual plan for carrying plates is to liave a j 

 number of dark slides, each made to hold two plates, I 

 which, of course, must be numbered, or a changing box 

 or bag may be used ; and it is necessary, therefore, to be 

 extremely careful to avoid exposing the same plate twice. 

 This occasionally happens, and it is a .source of serious 

 disappointment. In oi-der to a\-oid failure in this way, a 

 l)Ook should be provided in which a record should be kept 

 of each plate, stating number of plate, subject, time of 

 day, tlie size of stop (or diaphragm), the lens used, and time 

 of exposure. 



We must not omit a few words about instantaneous 

 ! 'I'ltography. If really instantaneous effects are reciuiri'd, 



111- kind of mechanical sliutter must be used, and these 



.;i be had in a variety of forms. One of the most simple 



IS a slide witli an adjustable aperture, which is arranged to 



fall in front of the lens, on being released at the re(]uired 



instant The time of tlie exposure can be regulated by the 



length of the aperture. Some very good effects may be 

 obtained by merely using the hand to remove the cap of 

 the lens, care being of course taken not to shake the 

 camera. 



FAIRY RINGS.* 



You demi-puppcts, that 

 By moonshine do the green soar ringlets make, 

 Whereof the ewe not bites. 



SCIENCE has been scarcely more explicit than Shake- 

 speare concerning the identification of these mysterious 

 demi-puppets, although many attempts at explanation have 

 been made. In spite of this, I have a theory of my own, 

 which, halting though it be, I here expound. 



I occupied during a few years a house on the slope of tJie 

 Hope Mountain, near C'aergwrle, in Flintshire. The 

 house is named " Celyn " in the Ordnance maps. It 

 commands a fine view of the Alyn valley and country 

 beyond. The most conspicuous of the pasture fields dis- 

 played below had no fairy rings during the first and second 

 years of my residence in the Celyn : but on the third a 

 large crop of them came into existence. They were 

 arranged in orderly rows, and so conspicuous that they . 

 forced themselves continuously on my attentiixt — were, '.in . 

 fact, almost irritating by their persistent appeals for ex- 

 planation. They w^orried me thus every day from the 

 September of one year to the July of the next, excepting 

 when the snow was on the ground. ^ 



I walked down frequently to the field and examined the 

 troublesome things, finding them always the same — viz., 

 nearly true circles, and composed of coarser grass than that 

 surrounding them, and at times with a crop of small fungi 

 dotted over them. They varied very little in size, were 

 about six feet in diameter — too small to have been the 

 track of any tethered animal — but they evidently had re- 

 ceived some kind of special manuring. 

 . Suddenly, on one bright July morning, the mystery was 

 solvcA A crop of grass had been mowed, tossed, and 

 ■winnowed, and was'now in cocks ready for carrying to the 

 stack. The circumference of the base of these cocks corre- 

 sponded almost accurately with that of the fairy rings ; 

 their numbers and arrangements wore nearly .identical ; 

 some of the cocks actually covered the ai-ea enclosed by 

 the ringlets of the demi-puppets. . i 



Then I remembered the liistory of the last year's harvest 

 on that particular field. A weary continuance of drench- 

 ing rain commenced just when the grass was cocked as now, 

 and it remaijied thus on the ground for several weeks, 

 until almost black with fungoitl rotting. Here, then, was 

 the explanation. The juices of the rotting grass had been 

 washed down the slopes of the cocks, and with these juices 

 were the fungus germs that " soured " the ground. 



There would thus be efFected a sort of special or dif- 

 ferential manuring of circles, having outside diameters 

 corresponding to that of the base of the cocks, and a thick- 

 ness of ring equal to the depth of penetration and drainage 

 of the rain. 



The last years history of tJiis field was impressed on my 

 memory by a small triumph of diktinnli- science applied 

 to agricidture. My own grass was cut at the same time 

 as the grass of this opposite field, and both were cocked 

 on Friday, in splendid weather ; but 1 had observed a 

 steady fall of the barometer, ami accordingly employed 

 extra hands, and made a great bustle to g«'t my hay 

 carried on Saturday — worked till midnight —thereby 

 amusing cousiderably my ncighboui-s, who were profes- 



• By W. Mattica Williams. From the (t'liitleiiiaii's ilaijazinr. 



