Recently some investigations by Haberlandt, Noll, Darwin and others have suggested an explanation which has much to recomrtiend it.
Noll, A Short History of Mexico (Chicago, 1903); Santiago Ramirez, Noticia historica de la riqueza mineira de Mexico (Mexico, 1884); Friedrich Ratzel, Aus Mexico: Reiseskizzen aus den Jahren 1874-1876 (Breslau, 1878); Matias Romero, Geographical and Statistical Notes on Mexico (New York, 1898); idem, Mexico and the United States (New York, 1898); E.
Noll adopts mercury because it is easily purified, and its physical condition in the liquid state is determinate; there is, however, a discontinuity involved in passing from the liquid to the solid state at a temperature of -40° C., and it cannot be used at all with some metals, such as lead, on account of the rapidity with which it dissolves them.
Noll employed mercury thermometers, but as he worked over a small range with vapour baths, it is probable that he did not experience any trouble from immersion corrections.
Within the last Kochlorine (Noll, 1872) with two species, and Lithoglyptes (Aurivillius, 1892) with three species, have since been included.