schlink: variance of measuring instruments 395 



Remarks. — One of the nearest allies of this genus is Mixornis 

 Hodgson, of which the type is Motacilla rubricapilla Tickell, 

 but Sterrhoptilus differs from this group in the very different 

 shape of the nostrils, which are not rounded as in Mixornis, 

 but narrow, almost slit-like, and very strongly aperculate; the 

 rictal bristles are much shorter and weaker; the bill is narrower 

 and more slender; the first primary narrower and about half the 

 length of the second; and the middle toe without claw is shorter 

 than the exposed culmen. All the species here referred to 

 Sterrhoptilus have the upper surface more or less streaked, not 

 plain as in Zosterornis whiteheadi; and furthermore there is no 

 white eye-ring in any of them. This new genus is of interest as 

 another instance of the wonderful variety of structure among the 

 babblers; and, furthermore, it adds another endemic genus to the 

 avifauna of the Philippine Islands. The species referable to 

 this group are as follows : 



Sterrhoptilus capitalis (Tweeddale). 



Sterrhoptilus plateni (Blasius). 



Sterrhoptilus dennistouni (Grant). 



Sterrhoptilus nigrocapitatus (Steere). 



Sterrhoptilus pygmaeus (Grant). 



TECHNOLOGY. — Variance of measuring instruments and its 

 relation to accuracy and sensitivity .^ Frederick J. Schlink, 

 Bureau of Standards. 



While the general concepts of accuracy and sensitiveness in 

 connection with measuring instruments are well known, certain 

 phases of the meanings of those two terms have not been clearly 

 differentiated, and the factor of variance which bears an impor- 

 tant relation to the two just mentioned has not hitherto been 

 given extended discussion or made susceptible of definite numeri- 

 cal expression. 



Accuracy and inaccuracy defined. An instrument is accurate 

 when its indications accord with the true values of the quantity 

 being measured. Perfect instrumental accuracy, then, is only an 



^ A brief presentation, based on the complete papernow in press, and to appear 

 as a Bureau of Standards Scientific Paper. 



