February 3, 1905.] 



SCIENCE. 



171 



scientific instruments, and have not only 

 shown how defects could be corrected, but 

 have developed the theory and the design 

 of many new instruments. All this has 

 occurred so recently that it is not gener- 

 ally known in the United States, and Ger- 

 man instruments are not as largely used as 

 they deserve to be. We hope that the next 

 few years may witness a similar impetus in 

 the production of scientific instruments in 

 this country, and that the United States 

 may come to hold the same enviable posi- 

 tion with respect to scientific instruments 

 in general that she now does with respect 

 to tools and labor-saving machinery and 

 to certain special classes of scientific in- 

 struments. 



The advantage of having instruments 

 and standards of high accuracy for engi- 

 neering and research work is obvious and 

 needs no proof. I wish, however, to point 

 out the advantage of using such instru- 

 ments as far as practicable for purposes of 

 instruction, especially in the more ad- 

 vanced laboratory courses. If the appa- 

 ratus is not accurately adjusted the careful 

 student and, perhaps, his instructor as well, 

 is prone to lose valuable time in trying to 

 locate errors that are inherent in the appa- 

 ratus, or in striving for a degree of accu- 

 racy which is unattainable with the instru- 

 ments employed. On the other hand, when 

 the apparatus is known not to be correct 

 it is so easy to attribute to the instruments 

 any discrepancies in the results that care- 

 less reading and hasty work may possibly 

 be encouraged. It is a great delight to the 

 real lover of quantitative experimental 

 work, of Avhom a great many are to be 

 found in almost any college class, to do a 

 piece of work with precision instruments 

 and obtain an accurate result, duly checked 

 by proper variations of the experiment. 

 The educational value of such work is cer- 

 tainly greater than when only roughly 

 done ; the pleasure derived is incomparably 



greater. It is by no means necessary that 

 all the instruments of a laboratory be sent 

 away to be tested. If only the laboratory 

 possesses correct standards and suitable 

 comparing apparatus, the calibration or 

 adjustment of most of the other instru- 

 ments furnishes excellent experimental 

 work for the students and assistants of the 

 laboratory. 



Another important section of the work 

 of the bureau is photometry. This is really 

 optical rather than electrical, but owing to 

 the fact that the chief work is with electric 

 lamps and a very considerable electrical 

 equipment is required, it is grouped with 

 the electrical in our organization. The 

 standards employed in photometric testing 

 are less satisfactory than in most other 

 branches of physical measurements. The 

 quantity of light emitted by a given source 

 is usiially expressed in candle power ; the 

 ordinary incandescent electric lamp, being 

 approximately equivalent to sixteen stand- 

 ard candles, is called a sixteen candle- 

 power lamp. The candle as a standard of 

 measure has passed out of vogue, but light 

 is still expressed in candle power. Various 

 sources of light have been proposed as 

 standards, the Hefner lamp burning amyl- 

 acetate, being most used as a primary 

 standard. As woi'king standards specially 

 prepared incandescent lamps are generally 

 used, and are quite satisfactory. Greater 

 progress has been made in recent years in 

 developing photometers and the auxiliary 

 apparatus for comparing lamps than in 

 perfecting a primary standard of illumina- 

 tion. Although the initial equipment of 

 the bureau for this work is not yet com- 

 plete, we have already done considerable 

 testing, especially in rating lamps to be 

 used as standards by manufacturers and 

 others, and in testing lamps purchased by 

 the various departments of the govern- 

 ment. Millions of incandescent lamps are 

 sold each year on carefully drawn specifi- 



