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THE POPULAR SCIENCE MONTHLY 



connecting of all fixtures, and even then 

 there is risk in applying it of flooding parts 

 of the house. " The peppermint test is use- 

 ful in a measure, but unless great care is 

 taken in applying it the results are at times 

 misleading. It is, therefore, in the hands 

 of inexperienced or unscrupulous persons a 

 rather dangerous and somewhat objectionable 

 test. It is not always possible to define by 

 it the exact position of the leak, or to deter- 

 mine exactly what the defect is. In the more 

 positive smoke test, on the other hand, any 

 leakage becomes apparent to the senses of 

 smell and sight ; in fact, in nearly all cases, 

 except where leaks are very slight, the issue 

 of smoke will indicate the exact point at 

 which plumbing is unsafe. In order to have 

 continued assurance that the plumbing and 

 the drainage and the gas-piping remain safe, 

 it is advisable to repeat the tests from time 

 to time. The walls of a building settle, the 

 pipe joints may become untight, or the joints 

 may open by expansion when much hot water 

 passes through the waste, or pipes may break, 

 or traps may sag or tip over, rubber gaskets 

 of floor joints may disintegrate and rot, leav- 

 ing open cracks through which sewer air may 

 pass, or joints made with brass couplings 

 may become loose, and rubber or leather 

 washers may rot ; in short, there are numer- 

 ous points which in a plumbing system may 

 become defective after it is in use for some 

 time. Hence the necessity of periodical re- 

 inspection, which is just as desirable with 

 plumbing work as it is with steam boilers or 

 other machinery." 



The Electric Arc In a lecture at the 

 Royal Institution on Electrical Illumination 

 Prof. J. A. Fleming exhibited the formation 

 of an arc between carbon rods, and said that 

 it had been experimentally proved that the 

 arc could not be started unless either the 

 rods were first brougiit into contact or the in- 

 sulating power of the air between was broken 

 down by an electric spark. An immensely 

 magnified imago of the arc was projected on 

 the screen, so that its interior structure was 

 rendered visible. It was seen, for instance, 

 that the positive carbon rod becomes most 

 intensely hot at the extremity and hollowed 

 out into the form of a crater, from which 

 about eighty per cent of the total light is 

 emitted. The negative carbon does not be- 



come so hot. The space between the two, or 

 the true arc, is filled with vapor of carbon. 

 In the central space a brilliant violet axis is 

 seen, violet being the color of incandescent 

 carbon. Outside this is an auraole of carbon 

 vapor of yellow or golden color. With the 

 use of a prism the central axis of the arc 

 gave a spectrum marked by two brilliant 

 violet bands. It was next shown that the 

 rise of electric pressure in the arc takes place 

 chiefly at the surface of the crater, which is 

 in fact the place where the work is done in 

 evaporating the carbon. The light emitted is 

 therefore due chiefly to the incandescence of 

 the carbon in the crater. Hence the light is 

 not given off equally in every direction. It 

 is most intense in tliat direction in which the 

 largest area of crater can be seen. 



Hnmniing Birds as Carriers of Pollen. 



The agency of humming birds in transferring 

 pollen from flower to flower is shown in a 

 paper by Joseph L. Hancock to be parallel in 

 importance with that of insects. The com- 

 mon ruby-throated humming bird, though it 

 is not endowed with specialized structures 

 for the specific performance of this office, has 

 in its mouth parts and feathers means for 

 harboring the pollen. The anatomical pecul- 

 iarities of its head permit access to flowers 

 of a wide range of forms. The bill, by vir- 

 tue of its flexibility, is capable of probing to 

 the bottom of most of the common forms of 

 flowers ; and in the feeding process the 

 flower is often bent over. The various ways 

 in whic-h pollen is carried to this bird were 

 revealed on microscopic examination of some 

 dead specimens. On the lower mandible just 

 in front of the angle of the mouth, over- 

 shadowed by the nasal scale when the bill is 

 closed, a faint yellowish line marks the de- 

 posit of pollen grains resting, clustered to- 

 gether, in a small groove. Pollen grains 

 work their way free to the summit or vanes 

 of the feathers, and are caught up by the 

 barbs of the feathers along the sides of the 

 chin and lores, where they remain ready to 

 be deposited when a more suitable surface 

 is presented. A second receiver of pollen 

 is the deep median groove under the lower 

 bill, the point of meeting of the rami. Four 

 ways have been observed by the author in 

 which pollen becomes engaged or held by the 

 feathers. In flowers, the pollen of which is 



