DIATOMS. 
BY ANDREW WAINE. 
ANY persons have heard of these beautiful objects 
and those who possess a microscope have no doubt 
often wished to have specimens to examine ; and the object 
of this paper is to tell them when, where, and how to collect 
and mount them in the most advantageous manner. 
The Diatomacee (for that is the name-of the group I in- 
tend to describe) may be collected always, as some one of 
the many varieties may be found in almost any pond or 
brook; but the most beautiful are found in the mouths of 
tidal rivers, or in fossil deposits. 
A diatom is characterized by having a flinty case or shell, 
beautifully marked with lines, or rows of dots; but these 
are often so fine and close together that they cannot be 
distinguished, except with a well-constructed instrument 
and high powers (a 4-inch objective will do for most), and 
this has led to the employment of some of these as test- 
objects—that is to say, that if one glass will define the 
markings better than another it is considered more fit for 
scientific purposes ; and so great is the difference between 
the size and distance apart of the markings, that some may 
be used as tests for the low powers, while others can only 
be used for the highest. 
Many of these beautiful forms can be found living in the 
Thames, and other rivers on our own coasts. In the months 
of April, May, September, October, and November, they 
will be found in the greatest abundance and variety; the 
salt marshes on the banks of most of the rivers will also 
well repay the trouble of searching for them. | 
Supposing the reader to be in London, and wishes to 
collect these interesting objects for himself, I should advise 
him to goto Southend (which may be reached by the 
Tilbury and Southend line, starting from Fenchurch street 
station), which is as good a place as any other for the pur- 
pose of collecting the objects under discussion; the mode 
of doing which is to gather the seaweeds at low tide, taking 
care to take as little sand with them as possible, and at 
once put them into a bottle of sea-water, if it is desired to 
examine the living forms in their natural position on the 
weed. But, if their flinty cases are wanted to exhibit the 
markings, the weeds may be put, dry, into a bag; and, on 
reaching home, they are to be plunged into a jar of fresh 
