vi PREFACE. 
matter I have dealt with has long been the common 
property of scientific teachers. 
I am much indebted to Mr. J. Cooper for the zeal 
and assiduity he has shown in carrying out my sug- 
gestions for illustrations. All the engravings, with 
one exception, were executed under his superinten- 
dence. 
ARABELLA B. BUCKLEY. 
Christmas, 1878 
