ABOUT MEASURES OF LENGTH. 657 



ing can be done from a distance of about eight metres (over twenty- 

 five feet) from the balance. In the room where standards of length 

 are compared, there is a comparator which cost about Xhree thousand 

 dollars, and another one is probably completed by this time, which is 

 worth five thousand six hundred dollars. 



It seems strange that the precise relation existing between the 

 imperial standard yard and the metre of the Archives is not known. 

 Nevertheless, it is true, for the two measures have never been directly 

 compared. No equation can be assigned to them that is not likely to 

 be erroneous by at least "005 of an inch ; but, in the year 1878, Par- 

 liament declared that the legal value of the metre, in inches, should be 

 39-37076. 



It may be thought that so small an error as five one-thousandths of 

 an inch, in a bar more than three feet long, is not worthy of serious 

 consideration ; but the fact is, that any error that can be detected by 

 the most refined instrumental means is of great consequence, espe- 

 cially for scientific work. The error mentioned above will appear 

 as a relatively large one, when we state with what accuracy minute 

 measurements may be conducted. Professor Rogers considers that 

 the error in comparing the length of two metre bars need not ex- 

 ceed the one-millionth part of a metre. In terms of an inch this error, 

 expressed in figures, would be 'OOOOOSO. In testing the performance 

 of his excellent comparator, he found the value of a centimetre, in 

 terms of an inch, to be "393707. The generally accepted value is 

 3937O8, which indicates a truly wonderful degree of accuracy in the 

 instrument. 



Professor E. W. Morley has made some experiments to determine 

 the probable error in micrometric measurements, and he has found 

 that the errors of a single observer, under the particular conditions 

 described, were very small. "With a low-power object-glass, the prob- 

 able error does not exceed thirty -nine ten-millionths of an inch. With 

 a greater magnifying power he found it to be about thirty millionths 

 of an inch. These errors, inconceivably small as they are, can be 

 made appreciable by means of a microscope. 







AEE CEMETERIES UNHEALTHY? 



By M. G. EOBINET. 



IF the tomb is characteristic of humanity, as Vico has said, the cem- 

 etery, M. Pierre Lafitte remarks, is absolutely necessary to all 

 human society. It not only furnishes a more or less hygienic method 

 of disposing of the bodies of those who are no more it is also a fun- 

 damental institution, in the sense that it is a symbol in no way arbi- 

 voL. XIX. 42 



