426 



THE POPULAR SCIENCE MONTHLY. 



often cut end polished and palmed off as 

 diamonds ; but this material is costly. A 

 composition for rubies is made of five hun- 

 dred parts of strass — a specially manufact- 

 ured glass — twenty parts of glass of anti- 

 mony, and a half-part each of purple of 

 Cassius and gold. Mock pearls are some- 

 times very deceptive in appearance, but 

 they can usually be detected by comparison 

 with the real gem, by their brittleness, or 

 by the clumsy and blunt-cdgcd appearance 

 of the drill-holes, which are usually perfect 

 in the real pearls. The scales of a small 

 fish known as the bleak have been used 

 in the formation of false pearls ; but as it 

 requires some eighteen thousand of these 

 Csh to provide one -pound weight of the 

 pearl-making material, the manufacture is 

 not likely to become extensive. 



Preventable Loss in igricnltnre. — In a 



British Association paper on this subject, 

 Professor W. Freame first described the 

 uncontrollable losses which were chiefly such 

 as were determined by meteorological con- 

 ditions. These, if they could not be antici- 

 pated, might to some extent be mitigated by 

 acting upon the recorded practice which had 

 been found most beueficial in similar cases 

 in previous years. Hence the value of such 

 records. Controllable losses were such as 

 might reasonably be anticipated, and there- 

 fore provided against, and should be in a 

 very high degree, although not absolutely, 

 preventable. The toleration of such pre- 

 ventable losses might be attributed partly 

 to ignorance, partly to indifference, and 

 partly to empiricism. First among the 

 sources of preventable loss was the imper- 

 fect working of the soil, which was a com- 

 mon cause of poor crops in the immediate 

 future and of worse trouble farther on. 

 Another source was the use of bad seed. 

 No greater folly could bo conceived than 

 that of introducing upon the land by means 

 of purchased seeds the seeds of weeds and 

 parasites. The most objectionable rubbish 

 was sometimes sown, and heavy expenses 

 were in consequence subsequently incurred. 

 A third source was the encouragement of 

 weeds, of which the most common species 

 were grown at immense cost to the farmer. 

 They robl^ed him just as much as a pick- 

 pocket did who stole his purse. Ilis object 



was, or should be, to concentrate all the 

 capacities of the soil upon the production of 

 useful crops ; every weed that was grown 

 detracted from this purpose. Ignorance of 

 the properties and affinities of weeds was 

 just as deplorable. Some — the cruciferous 

 weeds, for example — harbored and encour- 

 aged insect pests till the cruciferous crop 

 they were waiting for was ready to be de- 

 voured and destroyed by them. Another 

 source of loss was the deterioration of grass- 

 lands. There were in the British Islands 

 nearly thirty-three million acres of per- 

 manent or temporary grass land, which was 

 equivalent to three sevenths of the entire 

 area. Yet. as to the nature of the herbage 

 growing upon this enormous area, ninety- 

 nine farmers out of one hundred were in 

 entire ignoi-ance. A fifth source was from 

 pests. The maintenance of insect-thieves 

 sometimes constituted a severe drain upon 

 farming capital. Yet in no part of his edu- 

 cation was the farmer called upon to famil- 

 iarize himself with the habits of these creat- 

 ures. Of fungi pests, his knowledge was, 

 if it were possible, even less. Other sources 

 were diseases of live-stock, some of which 

 were preventable and some greatly reduced, 

 while others stood in need of further in- 

 vestigation ; and injudicious expenditure. 

 Among the most practicable remedies for 

 these preventable losses, and a means, there- 

 fore, for making agriculture a more profit- 

 able occupation, was the extension of sound 

 technical instruction in agriculture. 



Photography as an Aid to Astronomy. — 



Mr. A. A. Common believes that some as- 

 tronomical objects can be studied to better 

 advantage in photographs than in them- 

 selves. The brain can not always take in 

 the perceptions of the eye fast enough, and 

 the eye is not sensitive to images whose 

 brightness falls below a certain limit. In 

 photography, a prolonged exposure may be 

 made to compensate for deficiency in lumi- 

 nous power ; and the sensitive plate being 

 competent to respond to quicker vibrations 

 than the eye, it is possible to obtain photo- 

 graphs of celestial objects radiating ligiit 

 which the eye is not adapted to receive. 

 While the moon has received much atten- 

 tion, the photographs of it taken by Ruth- 

 erford, twenty years ago, have not been su- 



