58 



Dr. R. S. Clay. On the Application of 



obviously wrong. Otherwise the actual means were used so that the 

 error might be the more readily estimated. Had I been able to obtain 

 printed uniform patches I have no doubt the results would have been 

 better. But even these can leave no doubt of the approximate truth 

 of the law. 



A Blue Ink from Winstone. 

 Curve No. 20. I. A very faint rubbing. 



Curve No. 21. II. A little darker than I. 



