Temperature on the Viscosity of Gases. 217 



incomplete for this phenomenon, in the same general way as 

 are the analogous hypotheses regarding the compressibility of 

 gases and other phenomena. The hypothetical deductions 

 fail to accord completely with the results of quantitative 

 measurements, 



Discussion of Results of all Researches 

 on Air and C0 2 . 



The experimental results which I have given in the fore- 

 going tables, and the deduced equations, show that, unless 

 some considerable and regular source of error affects them, 

 the viscosity of both dry air (freed from C0 2 ) and carbonic 

 acid increases with the rise of temperature according to a 

 rate which varies with the temperature and is smaller as the 

 temperature is higher. The ratio rj t : jj is therefore not 

 proportional to the first power (Maxwell) of the absolute 

 temperature ; it is not expressible by a linear equation of the 

 first degree, e. g. Vt=Vo (! + &), where t — temperature C. and 

 b = & constant ; nor is it given by the equation r) t =rj (1 + 

 at) n , or its equivalent r) t -t-r) = cT n , where t= absolute tempe- 

 rature. The last three equations are the only ones thus far 

 used by observers in discussing their results, although the 

 work of E. Wiedemann and A. von Obermayer shows a 

 decided departure from these expressions. The insufficiency of 

 the latter equations may be shown by discussing the observa- 

 tional data by the logarithmic method which I used in my 

 former paper. Nor could the equation rjt^Vo (l + at) n be 

 more than an empirical equation at best, unless possibly when 

 a were expressed as a function of t and the pressure, a condi- 

 tion which I have not thought worth consideration at present. 

 For the expression of my own results, I have employed 

 merely the empirical equation with increasing powers of t, as 

 I have found no theoretical hypothesis which led to results 

 corresponding to the observed relation of rj and t. 



The deviation of both air and carbonic acid from the 

 equation v t =7] (l + bt) is so small, and the difficulties of precise 

 measurement so considerable, that these deviations may often 

 be masked by accidental errors of measurement, and by 

 " constant errors," arising from imperfect drying or purifi- 

 cation of the gas, from differences between the thermometer 

 indications and the actual temperature of the gas, from faulty 

 proportioning of apparatus, and from other sources. This 

 discussion of my own method in these regards I give at page 

 205 ; that of others, I cannot advantageously attempt. But I 

 will proceed to a review of the results obtained by all others 

 who have worked in this field : and shall show that for air and 



