102 



KNOWLEDGE. 



[May 1, 1695. 



are of the same size. If coins and glass plates be piled up 

 alternately, and the outer coins be connected with the poles 

 of the electric machine, perfect images are formed on both 

 sides of each glass. If several glasses be placed between 

 two coins, only two images will be produced, one on each 

 of the outside glasses. In all cases the glasses must be 

 scrupulously well cleaned with chamois leather. 



Heat will produce similar results by the molecular 

 bombardment to whjch the surface of the cold glass would 

 be exposed by the gases heated by the coin. If a very hot, 

 clean coin be placed on a cold mirror, and be removed 

 after being cooled down, nothing will be seen on the glass. 

 But if the mirror be breathed upon, an exact image of the 

 coin becomes visible. If the point of a blowpipe be passed 

 over a clean mirror, with sufficient quickness to prevent 

 the sudden heating from breaking it, nothing is seen after 

 the glass is cold. But if you breathe upon its surface, the 

 track of the flame is clearly marked. While most of the 

 surface looks white in consequence of the light reflected by 

 the deposited moisture, the track of the flame is quite 

 black. But under a microscope this track is discovered to 

 be wet with a thin, even film. If the jet of the blowpipe 

 be tracked over the mirror so as to form figures, the 

 breath on the cold plate will reveal the figures, traced with 

 great distinctness. The hot coin in some way seems to 

 alter the dust-particles on the mirror, causing them at 

 certain parts to reflect more light than at others, to be 

 brought out more plainly when the moist breath develops 

 them. 



Probably all polished surfaces may be similarly affected. 

 A plate of quartz gives most beautiful images, perfect in 

 details, retaining their freshness longer than those on 

 glass. If a piece of mica be split, and a coin be slightly 

 pressed for half a minute on the new surface, without any 

 current of electricity or application of heat at all, a 

 breath-figure of the coin is left behind. If a leaf of 

 paper, printed on one side and thoroughly dry, be placed 

 between two plates of glass, and left for ten hours either in 

 the daylight or in the darkness (a slight weight being placed 

 over to keep the paper even), nothing is seen ; but as soon 

 as you breathe on the glass, a perfect breath-impression is 

 made of the print on both pieces of glass. These are 

 generally white, and are most easily produced during keen 

 frost. If paper devices be placed for a few hours under a 

 plate of glass, clear breath-figures of the devices will be 

 produced when you breathe on the glass. After an ivory 

 point has been traced in any shape over a glass plate with 

 slight pressure, a black breath-figure of the writing is made 

 at once. If plates of glass lie for some hours on a table- 

 cover which has on it figures worked in silk, strong white 

 breath-figures are impressed on the plates, the silk coming 

 out white and the cotton black. 



Some exceedingly curious permanent illustrations of 

 the phenomena are to be found. There are several im- 

 pressions of brasses in the basement under Henry IV. 's 

 chantry in Canterbury Cathedral. On the walls appear 

 shapes of the effigies. Sometimes the stone is unstained 

 all over the area of the figure, but surrounded by a broad, 

 dark smudge ; and in other cases the reverse is found, 

 the area of the figures being indicated by a uniform dark- 

 tint, whilst the surrounding stone is unstained. Friends 

 of Mr. Croft, who can be trusted for their authentic 

 evidence, give two remarkably interesting cases of breath- 

 figures of this permanent description^ The plate-glass 

 window of a hotel in London has on the inside a screen 

 of ground-glass lying near, but not touching ; upon the 

 latter are the words " Colfee Eoom " in clear, unfrosted 

 letters. When the screen was taken away the words were 

 left plainly visible on the window, and no washing would 



remove them. A house in London had been a hotel three 

 years before ; on one of the windows had been a brown 

 gauze blind, with the gilt letters "Coffee Eoom" on it. 

 On misty days the words " CoS'ee Eoom " are distinctly 

 seen, but not on other days. This is a marvellously 

 accurate instance of permanent breath-figures, the mist 

 acting like the breath, depositing the moisture on the 

 glass. There is no doubt that a little observation on the 

 part of our readers would reveal many curiosities of this 

 kind in old houses, or at railway stations. 



No one, as yet, has clearly explained how these im- 

 pressions are produced by electricity and heat. The fact 

 always confronts us that the simpler the phenomena the 

 more difficult is the explanation. 



ON THE TWO FORMS OF PRIMROSE, 



By the Eev. Alex. S. Wilson, M.A., B.Sc. 



IF a number of common primroses be examined, they 

 will be found to consist of about equal proportions of 

 two kinds of flower, differing somewhat from each 

 other. In one set, the '• pin-eyed " as they are called, 

 the centre of the flower is occupied by a round knob 

 resembling the head of a good-sized pin; this is the stigma 

 or extremity of the seed-vessel, to which the pollen is 

 applied in fertUization. Externally, the anthers of the 

 pin-eyed primrose are not visible, since they stand midway 

 down the inside of the flower-tube. A flower of the other 

 or •' thrum-eyed" form has the relative positions of these 

 organs reversed ; at the mouth of the flower are the five 

 anthers, while the stigma, which is situated halfway down 

 the tube, cannot be seen without cutting open the corolla. 

 Vertical, sections of the flowers show that in the pin-eyed 

 form the slender cylindrical style which supports the 

 stigma is almost as long as the flower-tube ; the style in 

 the other form is much shorter, and only reaches halfway 

 up the tube. The former is, therefore, designated the long- 

 styled, the latter the short-styled, and the primrose is 

 described as heterostyled or dimorphic, ordinary blossoms 

 being homostyled or monomorphic. The point of special 

 importance to notice, however, is that the stamens of the 

 long-styled flower stand at a level which exactly corresponds 

 with tliat of the stigma in the short-styled form ; the 

 stamens of the latter, in like manner, are on a level with 

 the stigma of the long- styled flower. 



These two forms of primrose had long been known, but 

 their significance was never understood until explained by 

 Darwin in his paper " On the two forms or dimorphic 

 condition in the species of Primula, and on their remark- 

 able sexual relations," published in 1802. Since that time 

 Scott, Hildebrand, MiiUer, and others have repeated and 

 extended Darwin's experiments on dimorphic flowers, 

 confirming his conclusion that the two forms are adapted 

 foi- mutual cross-fertilization. 



Arrangements exist in many blossoms which secure the 

 transference of the pollen to the exact part of an insect's 

 body in one flower which is most likely to touch the stigma 

 of the next flower visited by the insect, and the floral 

 mechanism for this pm'pose often attains a remarkable 

 degree of precision. The dimorphic condition might 

 almost be described as a contrivance of the same kind. 

 The salver-shaped corolla of the primrose is evidently 

 fashioned in relation to the visits of insects ; its broad 

 limb, or upper horizontal portion, furnishes the attractive, 

 coloured surface which renders the flower visible from a 

 distance ; it also oft'ers a convenient landing-stage on 

 which the visitor can rest while dippmg its proboscis into 

 the flower-tube. Short-hpped and otherwise undesirable 



