October, 1910. 



KNOWLEDGE. 



405 



which goes to form a stalactite (whether in a hrne- 

 stone cave or under a damp arch) is soft and that it 

 onlv becomes crvstalHne by degrees, whereas the 

 stalactite formed from lime-water grows by a method 

 of crystallisation, as may easily be seen in 

 Figure 2, which is a microphotograph of the growing 

 point of the tube, in which the magnification is 

 about thirt\-eight diameters. It somewhat resembles, 

 except in rate of formation, a " frond " of crystalline 

 sal-ammoniac, as seen grow ing on a glass slide under 

 a microscope, and it is in striking contrast to the 

 soft amorphous deposit of calcium carbonate one so 

 often sees in lime-water. Again, the deposition of 

 the calcium carbonate, which goes to form a 

 stalactite, as stated in the above extract, is due to 

 loss of carbonic acid gas, and takes place at the 

 " base "" of the drop : but as may be seen on an 

 examination of the drop in Figure 1, the " claws " of 

 the crvstalline gro\\ th nearly encircle the drop, and 

 it appears almost as if the extension of this crx'stalline 



growth was due to and coincident with the absorption 

 of the carbonic acid gas of the air b\- the lime-water ; 

 a suggestion which is supported b}- the fact that the 

 drop of lime-water remains absolutely clear and 

 bright through all the stages of its formation, none 

 of the milkiness usualh" caused bv prolonged 

 exposure to the air being apparent. 



It would be strange indeed if the causes of forma- 

 tion of the two kinds of stalactites should be of such 

 an opposite nature, viz : in one case the loss, and in 

 the other the absorption, of the carbonic acid gas of 

 the atmosphere, but one seems forced to that conclu- 

 sion unless, as is just possible, both processes take 

 place in the case of the drop of lime-water, the gas 

 being absorbed in the earlier stages of its formation 

 and lost in the later stages, as the water in the drop 

 evaporates ; but if this explanation were the true one, 

 the drop would be milk\- in the earlier stages of its 

 growth, whereas, as already stated, this does not 

 appear to be the case. 



QUERIES .AND ANSWERS. 



Readers arc invited to send in Onestious and to ansK'cr the Queries "ui'liicJi arc printed on tliis page. 



QUESTIONS. 



2 (page 288), 7 and S (page 354) still remain unanswered. 



9. DYN.'\MO .\ND MOTOR.— -A continuous current 

 motor which is to worii at a rate of 100 H.- Power is to be 

 driven by energy conveyed by means of a conductor whose 

 resistance is 100 ohms, with a waste of not more than ten per 

 cent, of the energy supplied by the dynamo. What must be 

 the E. M. F. in the dynamo and the back E. M. F. in the motor ? 

 How many calories are produced per hour ? 



EXOL'IRHR. 



that if the sealing wax is held in frout of the jet the back 

 half of the front drops would be negatively electrified and 

 the front half of those immediately behind them be positively 

 electrified and that those would thus attract each other. But 

 why should the drops repel each other when the sealing wa.\ 

 is brought nearer ? I also do not understand why the former 

 case should explain the large size of drops in a thunderstorm 

 (pp. 99-1001. If rain drops fall from a positively electrified 

 thundercloud would they not all have the same sign and thus 

 repel each other ? 



A. T. 



REPLIES. 



10. WATER AND ITS OWN LEVEL.— The subjoined 

 problem was submitted to me by a young friend : — " It is 

 strange that water is said to find its own level, and yet the 

 surface of the world, about two-thirds of which is water, is 

 round." ,, ,, ,, 



11. A BOOK ON WASPS.— I have to thank "Biologist ■■ 

 for the information he gi\es about wasps ; would he further 

 oblige me by referring me to a really good book on the 

 natural history of these insects ? For the last two years our 

 school children have earned 2d. for each queen wasp killed, 

 besides prizes to the three who have killed the largest num- 

 bers ; this year they killed o\er 650, with the result, up to the 

 present, of a sensible diminution of the wasps seen as compared 

 with previous years. I am inclined to think that I have now 

 and then seen other wasps besides queens, in the late spring, 

 and which I presume must have survived the winter. 



JOHN GLAS. SANDEMAN. 



12. ELECTRIFIED WATER DROPS.— In Professor Boys' 

 "Soap Bubbles," p. 91, Figure 42 shews how the previously 

 scattered drops of a water jet coalesce on the approach 

 of an electrified stick of sealing wax. I can understand 



3. In reply to the question No. 3 in the August issue (page 

 301) I may say that January. 1907. was marked in Eastern 

 Europe with \'er>- great pressures. We ha\-e had on sea 

 shore : — 



The figures (in mm.) are taken from A. Klossovsliy Foun- 

 dations of Meteorology (Russian) [Odessa, Mathesis, 1910] . 



A. ORLIXSKV. 



5. In reply to the enquiry of " T.M." in the August number 

 he cannot I think do better than obtain one of PJiilips' 

 Planispheres, which will give what he is wanting for any 

 time on any day throughout the year. It can be set in a 

 moment to any date and time. I have often found it most 



"'^'^^"'- WM. L. JEFFERY. 



[Note. — We hope to republish an old map that gives the 

 details required. — Eds.] 



