August 1, 1891.] 



KNOWLEDGE 



147 



or highly inclined fissures, and are so named on account of 

 their resemblance to walls (Scnttice, dykes). When the 

 surrounding rock has decayed, the dykes may be seen 

 projecting above ground exactly like walls. Sometimes 

 the eruptive rock has followed the course of a " fault" ; 

 but in Scotland, at least, the vast majority of dykes rise 

 along ordinary fissures which, having caused no displace- 

 ment, cannot be considered as " faults." On the contrary, 

 the dykes may be traced undeflected across some of the 

 largest " faults." Dykes differ from veins in the greater 

 parallelism of their sides, their verticality, and greater 

 general regularity. Usually a dyke cannot be traced far, 

 but the well-known Cleveland Dyke, in the north of 

 England, runs for at least 60 miles, cutting through 

 various " formations " till it reaches the Yorkshire coast, 

 200 miles or more from the sheets of Miocene trap-rock 

 with which it is probably connected. The south-western 

 half of Scotland, and the northern parts of England are 

 ribbed across with thousands of dykes which seem to be 

 connected with the volcanic chain of the inner Hebrides 

 (of Tertiary age). The fissures through which such dykes 

 forced theu- way were not made by the molten matter 

 itself, but more probably were the result of violent 

 explosions and earthquakes proceeding from a region of 

 volcanic action. 



I must now conclude this paper, leaving the reader to 

 judge if I am warranted in applying the trap-dyke theory 

 to the lunar streaks. It certainly harmonizes lunar and 

 terrestrial phenomena, and suggests a close connection 

 between radiating streaks, chains of lunar volcanos, 

 mountain ranges, and ridges or lines of hills near the 

 volcanos. 



Kemakks by a. C. Eanyard. 



If the reader will turn to the photographs of the Moon, 

 published in Knowledge for May, 1890, and October, 

 1889, he will see that the rays or streaks have not 

 sharply defined edges as they presumably would ha\e if 

 they were trap-dykes. The rays vary in breadth, many 

 being from twenty to thirty miles broad, with very soft 

 nebidous edges. The whiteness of the rays in some cases 

 may be seen to degrade gradually from a narrow, sinuous, 

 bright band which runs along their centres — see, for 

 example, the two rays from Tycho that run across the 

 Mare Nubium, shown in the plate published in the May 

 number for 1890. The rays seem in no way to interfere 

 with the forms of the craters and irregularities of the 

 hmar surface, as we should expect to find them interfering 

 if they corresponded to a wall of injected rock either 

 harder or softer than the surrounding material. A good 

 instance of a broad ray passing over craters and rough 

 ground without aft'ecting the forms of the craters and 

 mountains is shown in photograph No. 1, plate No. 1, in 

 the October number for 1889, where a strikingly bright ray 

 radiating from Tycho passes across the rough ground to 

 the south of the Mare Nectaris and then across the plain 

 and onward. 



Lava streams and volcanic regions on the earth are 

 generally dark as compared with the surrounding rocks, 

 but the light-reflecting character of these rays cannot 

 be accounted for unless they are capable of reflecting 

 more light than light sandstone, or oven than chalk. 

 For the light -reflecting power of the Moon, taken as a 

 whole, about corresponds to that of light sandstone. See 

 the often quoted observation of Sir .lohn llerschel, who 

 compared the light of the nearly full Moon with that 

 reflected from Table Mountain at the Cape. Everyone 

 is familiar with the whitish appearance of the Moon as 



seen in the day-time. It appears hke a small whitish 

 cloud. 



There are many large dark areas upon the Moon, conse- 

 quently the brighter parts must be relatively white as 

 compared with light sandstone. It is true that the 

 summits of lunar mountains and craters differ greatly as 

 to their whiteness, but few terrestrial mountains are 

 wholly covered with snow, and, as seen fi-om a distance, 

 their whiteness would depend upon the amount of rock 

 surface and shadow intermixed with the snow. The 

 Moon, as a whole, reflects a little less than a quarter 

 of the light reflected by fi-esh fallen snow. My argument 

 is that the brighter patches and rays are so bright as 

 compared with the rest of the Moon's surface that their 

 whiteness cannot difl'er greatly from the whiteness of 

 snow. 



THE CHEMISTRY OF THE DAIRY. 



Dy Vaughan Corxish, B.Sc, F.C.S. 



IT is often felt as a disappointment by persons who 

 have been at some pains to acquire a knowledge of 

 the principles of chemistry, that the chemistry of the 

 breakfast table remains still beyond their ken. Com- 

 mon salt presents no difficulty, but what are mustard 

 and pepper, sugar, milk and butter ? Many a chemist has 

 had his breakfast spoilt by being called upon to explain 

 the composition of these things when he would rather be 

 availing himself of their nutritive properties. The " Pro- 

 fessor at the Breakfast Table " may sometimes indulge the 

 didactic vein, but only in a moment of imusual rashness 

 will the professor attempt an untechnical exposition of the 

 constitution of organic bodies. The reason is not far to 

 seek. The number of organic substances is very large, 

 being reckoned, indeed, by thousands. The great majority 

 of these consist of carbon and hydrogen, of carbon, hy- 

 drogen, and oxygen, or of these three elements together 

 with nitrogen. A mere statement of the elements con- 

 tained in the substance gives practically no information as 

 to its nature. Each chemical substance is made up of a 

 number of small parts, the fnulcnths. The properties of 

 the substance are determined principally by the properties 

 of the molecules. The molecules of organic substances are 

 differentiated from one another, chiefly by the number of 

 atoms in the molecule, and by the mode of arrangement of 

 these atoms, rather than by the nature of the atoms them- 

 selves. The connection between the arrangement of the 

 atoms and the properties of a substance is subtle and intri- 

 cate, and the experiments required for the discovery of the 

 mode of arrangement of the atoms are complicated and 

 ditiicult to follow. There is no royal road to this branch of 

 knowledge ; a general grasp of organic chemistry can only be 

 gamed through the laborious study of detail. It is iMSsible, 

 nevertheless, to impart a certain amoimt of information 

 concerning the chemistry of foods without demanding this 

 knowledge of details. It is true that the acquaintance 

 which is thus gained is far from being satisfying to the 

 enquiring mind, but it is nevertheless thus far satisfactory 

 that it has a definite practical value. 



The present article, within the limits we have indicated, 

 deals with the chemistry of milk and of the food-stuff's 

 prepared from it. Milk may be described as an emulsion, 

 its opacity being due to the dissemination throughout its 

 bulk of a great number of small globules of fat. This fat 

 swims in a watery fluid, not pure water but an aqueous 

 solution of caseine, milk sugar, and a small amount of 

 inorganic matter consisting chiefly of common salt and 

 phosphate of lime. In the study of milk, cream, butter 



