t64 



SCIENTIFIC NEWS. 



[Sept. 1st, i8 



ally from the mark on one edge of the board to the mark on 

 the other edge, and the length of this diagonal will be the 

 diameter of a third pipe or circle which shall have an area 

 equal to the areas of the two pipes or circles -whose diame- 

 ters were marked on the board. 



COLOURED GLASS IN THE UNITED 

 STATES. 



UNTIL quite recently but little coloured glass, with the 

 exception of common black and amber bottles, was 

 made in the United States. Now quite a number of glass- 

 works are engaged in its manufacture exclusively, and at 

 others it forms a large part of the product. The colouring 

 materials most largely employed are iron, manganese, copper, 

 cobalt, and gold. These are generally used as oxides, though 

 in some cases, but very rarely, other compounds are used. 

 In addition to the above, arsenic, uranium, chromium, and 

 silver are occasionally employed. As was pointed out by 

 Bontemps many years ago, the colouring properties of the 

 metallic oxides are greatly modified by the degree of heat 

 to which the glass is subjected, and by other circumstances. 

 Not only will different temperatures give different shades 

 of the same colour, but even different colours. Manganese, 

 for example, which is the great decolourizer of glass, 

 so universally used for the purpose as to be known as 

 " glassmaker's soap," is used as a colourer, chiefly to im- 

 part a pink or purple to glass. If, however, the glass so 

 coloured remains too long in the furnace, it becomes pale 

 or reddish brown, then yellow, and finally green. From the 

 oxides of iron all the colours of the spectrum may be pro- 

 duced, and in the order in which thej' appear in the spectrum. 

 Its primary effect upon glass is to give it a green tinge. 

 Hence in the manufacture of white glass sand containing 

 much iron is carefully avoided ; what little it does contain — 

 and there is always more or less present — is neutralised by 

 the oxide of manganese. Oxide of iron, however, produces 

 other colours than green. Indeed, the green of this oxide 

 has but little brilliancy, and when rich emeralds are desired 

 other uia;:erials are used, such as oxide of copper. Iron 

 will produce in enamels, which are only glasses, a fine pur- 

 plish red, or, under a stronger heat, an orange. If a piece of 

 iron is thrown into the pot of a flint-glass house, during the 

 blowing, the glass in its neighbourhood will be orange or 

 yellow. In window-glass houses, the addition of a small 

 proportion of oxide of iron gives a bluish tint to the glass, 

 while it is well known that the glass left in the pots of the 

 bottle-houses becomes an opaque blue. Oxide of copper is 

 chiefly used to produce reds, rubies, and purples in the 

 cheaper kinds of glass. To produce these reds with copper, 

 however, requires skilful manipulation, as they are not all 

 fixed. The temperature must be kept at the lowest possible 

 point, otherwise the glass changes to a purple, then to a sky 

 blue, with a tendenc}' to green. A heat between the mini- 

 mum which gives a blue and the maximum which gives a 

 red, produces a purple. The finest rubies, reds, purples, 

 violets, etc., are produced by gold. The purple of Cassius 

 (which is a mixture of the oxides of gold and tin), or some 

 similar preparation of gold is used. The colouring power 

 of gold is so great that one pari of gold will give a full, rich 

 body of colour to from 600 to 1,000 parts of glass. The 

 glass coloured with gold can be made to assume a scarlet, 

 carmine, rose, and ruby. Cobalt gives a blue which is un- 

 alterable in any fire. It is also used for some of the finer 

 blacks. Carbon, usually as powdered cannel coal, is the 

 colouring matter chiefly used in the manufacture of black 

 and amber bottles. Plumbago was at one time largely used, 

 and is still to some extent. — Mineral Resources of United 

 States. 



THE ROYAL INSTITUTION. 

 The Element of Truth in Popular Beliefs. 



THIS formed the subject of a weekly evening lecture by Dr. 

 Lauder Brunton ; — 



The common saying, " Seeing is believing," gives a clue to the 

 origin of many popular delusions, for the evidence of our eyes 

 is by no means to be trusted, and unless corrected by the ob- 

 servations derived from other senses, will often prove deceptive. 

 Some popular beliefs are correct in regard to fact, but erroneous 

 in regard to interpretation. Some others, which in their present 

 form are absurd, are the survivals, or modifications, of other 

 beliefs which were true. 



In endeavouring to discover the element of truth in any 

 belief, we may be aided by tracing its history backwards in 

 time, or by comparing it with allied forms of ^belief in different 

 places. 



As an example of the historical method, we may take the 

 belief that horse-flesh is unfit for food, a delusion which arose 

 from the circumstance that horse-flesh was unfit for Christian 

 food, inasmuch as the horse was sacred to Odin, and eating its 

 flesh was a sign of Paganism. 



As an illustration of the comparative method, we may take the 

 belief that a person cannot die if any door in the house be 

 locked. Other forms of the belief are that a person cannot die 

 as long as the doors or windows of the room in which he is lying 

 are closed, and observation enables us to ascertain that this is 

 due to the fact that the room is thus kept warm, and life there- 

 fore prolonged. 



The belief that disease may be cured by hanging up rags in a 

 sacred place may be connected, by intermediate forms, with the 

 fact that infectious diseases may be conveyed from one to 

 another by articles of clothing. 



Some omens probably have an historical origin. Others de- 

 pend on physical conditions, such as stumbling on leaving the 

 threshold as an indication of coming misfortune. This may be 

 regarded as simply an evidence of a deficiency in the motor 

 power of the individual which may cause him to fail in an 

 emergency. 



Others, again, may be referred to indistinct sensations or 

 sub-conscious conditions. Dreams are frequently influenced by 

 the circumstances of the dreamer, either at the time or some 

 days before, and hallucinations, as well as visions of ghosts and 

 fairies, may be regarded as forms of waking dreams. 



The signs which were regarded in the Middle Ages as dis- 

 tinctive of witchcraft, are now looked upon as symptoms of 

 hysteria, and the condition of hysteria may perhaps be defined 

 to be one in which impressions, originating within the body itself, 

 tend to overpower those transmitted from without by the usual 

 sensory channels. 



The phenomena of thought-reading and of the divining rod 

 may in many cases be explained by the fact that sensory impres- 

 sions may be received, and may lead to action, without rising into 

 complete consciousness in the individual who receives them. 



Etiology of Scarlet Fever. 



PROFESSOR EDWARD E. KLEIN, F.R.S., gave an even- 

 ing lecture on the above subject. He said that among the 

 infectious or zymotic diseases there are two, at any rate, 

 — namely, scarlet fever and diphtheria — of which it may 

 be said that their spread is, to a lesser extent, dependent on 

 defective domestic sanitation than is the case with 

 some of the other zymotic diseases, as, for instance, typhoid 

 fever. Indeed, it is maintained by competent authorities that 

 scarlet fever and diphtheria do not invade houses of faulty 

 sanitation with greater frequency or severity than those of per- 

 fect sanitary arrangements. This view is based on the impor- 

 tant experience gained during the past twenty years — viz., that 

 epidemics of scarlet fever and diphtheria have been brought 

 about by milk. He then stated, by way of explanation, that a 

 fact well established and needing no further comment is that 

 scarlet fever and diphtheria are, like small-po.\-, measles, whoop- 

 ing cough, and typhus fever, communicable directly from person 

 to person. This mode of infection, doubtless an important one, 

 and coming into operation in single cases wherever the elemen- 

 tary rules of isolation and disinfection are transgressed, alto- 

 gether sinks into insignificance when compared with the infection 

 produced on a large scale, if a common article of diet like milk 



