NOTES. 



43i 



seaward at high water, and will swing back 

 landward at the ebb. At sixty miles away 

 from the Atlantic coast the deflection due 

 to tidal action of this kind is probably quite 

 as great as the greatest deflection due di- 

 rectly to the moon. These flexures are not 

 confined to the surface, but must extend in 

 almost equal degree beyond the depth of 

 the deepest mine. Until the atmospheric 

 pressure and the state of the tides at each 

 moment can be accurately known for a great 

 distance around any given spot, the experi- 

 mental determination of the lunar disturb- 

 ance of gravity is out of our reach ; our in- 

 strument, even in the most favorable site, 

 must needs record incessant variations of 

 which no satisfactory account can be given. 

 A gravitational observatory must, therefore, 

 for the present content itself with register- 

 ing the more or less irregular tremors of the 

 earth that are allied with earthquake-move- 

 ments. 



English and Metric Measures. The fol- 

 lowing comparative summary of English 

 and French (or metric) standards of meas- 

 ures and weights will be useful : The Eng- 

 lish inch is equivalent to 2'5-i centimetres ; 

 the foot to 30 - 48 centimetres ; the yard, to 

 94*44 centimetres; the mile to 1609 - 33 me- 

 tres ; the nautical mile, to 1852"30 metres. 



The square inch is equivalent to 6 - 45 

 square centimetres ; the square foot, to 

 929'01 square centimetres ; the square yard, 

 to 8364 , 13 square centimetres. 



The cubic inch is equivalent to 16 , 3S7 

 cubic centimetres ; the cubic foot, to 28"516 

 cubic decimetres ; the cubic yard, to 764 - 535 

 cubic decimetres ; the pint, to 0'567 cubic 

 decimetre; the gallon, to 45*410 cubic deci- 

 metres. 



The English grain is equivalent to 64*799 

 milligrammes ; the ounce avoirdupois, to 

 2S-349 grammes; the pound, to 453'590 

 grammes ; the ton, to 1016-050 kilogrammes. 



The foot-pound is equivalent to 0'13825 

 kilogrammetre ; the French horse-power, to 

 75 kilogrammetres a second ; and the Eng- 

 lish horse-power (550 foot-pounds a second, 

 or 33,000 foot-pounds a minute), to 76 kilo- 

 grammetres a second. 



The metrical unit of pressure is the kilo- 

 gramme per square centimetre. We may 

 also count by centimetres of mercury or by 

 atmospheres. A pressure of one atmosphere 



corresponds to a column of mercury 76 cen- 

 timetres high, or to 1'033 kilogramme per 

 square centimetre. The English pound per 

 square inch corresponds with 70"3 grammes 

 per square centimetre. 



False Fangs in Harmless Snakes. The 



blowing-viper or puffing-adder of the United 

 States, although it is timid and unaggressive, 

 and can rarely be provoked to bite, and 

 then does no particular harm, has been 

 reputed a dangerous and venomous reptile 

 because it has long, fang-like posterior 

 teeth. It belongs to the genus Heterodon, 

 which is so called on account of this un- 

 usual and irregular dentition. It is of the 

 same group as the Xenodons, or strange- 

 tooths, of tropical America, which are also 

 supposed there to be poisonous, possibly 

 for no better reason than our North Ameri- 

 can genera are. Dr. Stradling allowed one 

 to bite him, and suffered no ill effects from 

 the wound. Mrs. Catharine C. Hopley states, 

 in " Land and Water," that she has lately 

 examined one of these strange - toothed 

 snakes for the purpose of seeing the fangs, 

 when she observed that they are mobile, 

 or what are called in the viperine snakes 

 hinged teeth that is, they are so set that 

 the snake can erect or depress them at 

 pleasure by a volitional movement of the 

 jaw. It is known, she says, that no poison- 

 gland exists in this snake, " and it was only 

 on venturing to feel the teeth, in order to 

 judge of their relative sizes, that the reptile 

 let me know it had a larger pair safely 

 tucked away in case I took too many liber- 

 ties." 



NOTES. 



A step toward fixing a system of uni- 

 form standards of time was made by the 

 convention of railroad managers which was 

 held at St. Louis, April 11th. Hour-lines 

 were agreed upon at fifteen degrees of longi- 

 tude apart, to which the clocks in the dis- 

 tricts respectively appertaining to them shall 

 be made to conform. Four standards were 

 made: Eastern time, to agree with that of 

 the 75th meridian ; central time, one hour 

 slower, to be regulated by the 90th me- 

 ridian ; and two other standards, two and 

 three hours slower than Eastern time, to be 

 fixed by the 105th and 120th meridians. 

 All changes in time will be made at the ter- 

 mini of roads or at the ends of divisions. 



