FRAGMENTS OF SCIENCE. 



715 



is written in English, and the second letter 

 from America is written in French. The 

 correspondence thus commenced is continued 

 as begun, alternating the two languages ; also 

 all letters received which are written in the 

 language of the receiver are returned care- 

 fully corrected to the writer. Thus, if letters 

 are filed, at the end of the year each student 

 has model letters in the foreign tongue, and 

 his own corrected letters for careful study. 

 In Swarthmore College, Pennsylvania, about 

 thirty students are enrolled as correspond- 

 ents. The letters as received are read aloud 

 in class, sometimes translated, sometimes in 

 French, and are made most interesting topics 

 for the lesson of the day. No one who has 

 not tried the system can fully realize the new 

 life and spirit that are thus infused into the 

 class. Instead of being a dry and dull 

 granunatical lesson, with little direct practical 

 bearing upon daily life, the language is seen 

 at once to have a life and meaning before 

 little expected by the student." 



The Liquefaction of Hydrogen. — At a 



recent meeting of the Royal Society, Pro- 

 fessor Dewar read a paper describing the 

 method by which on Tuesday, May 10th, he 

 had succeeded in liquefying hydrogen, the 

 last of the so- called "permanent gases." 

 The apparatus used was a year in building, 

 many slight but important details going to 

 make up the final successful machine. The 

 hydrogen was cooled to — 205° C. and then 

 allowed to escape continuously under a pres- 

 sure of one hundred and eighty atmospheres 

 from the nozzle of a coil of pipe at the rate 

 of ten to fifteen cubic feet a minute, into a 

 vacuum vessel doubly silvered, which was 

 itself surrounded with a space kept below 

 — 200° C. With these arrangements liquid 

 hydrogen began to drop from this vessel 

 into a second vacuum space, doubly isolated 

 by being inclosed in a third, and in five 

 minutes twenty cubic centimetres of liquid 

 hydrogen were collected. The yield of 

 liquid was about one per cent of the gas. 

 The liquid was clear and colorless and 

 showed no absorption spectrum. When a 

 long piece of glass tubing sealed at one end 

 and open to the air at the other was im- 

 mersed in the liquid hydrogen, solid air im- 

 mediately appeared in it ; and when a speci- 

 men of purified helium in a sealed tube was 



immersed, a distinct fluid was seen to collect 

 in it. It would seem from this that there is 

 little difference between the boiling points 

 of helium and hydrogen. Professor Dewar 

 pointed out that all known gases had now 

 been condensed into liquids which could be 

 manipulated at their boiling points under 

 atmospheric pressure in suitably arranged 

 vacuum vessels, though even so great a man 

 as Clerk Maxwell had doubts as to the pos- 

 sibility of ever liquefying hydrogen. With 

 liquid hydrogen as the cooling agent a tem- 

 perature could be reached within 20° or 30° 

 of the zero of absolute temperature, and 

 its use would open up an entirely new field 

 of scientific inquiry. M. Moissan read a 

 similar paper before the Academy of Science 

 in Paris early in May. It is also claimed 

 that Professor Olszewski had previously de- 

 termined the boiling point and critical tem- 

 perature of hydrogen. 



Grasses in Iowa, Nebraska, and Colo- 

 rado. — Prof. L. H. Pammel, in his Notes on 

 the Grasses and Forage Plants of Iowa, Ne- 

 braska, and Colorado, remarks on the differ- 

 ent aspects the forage question in central 

 Iowa presents now from what it did fifteen 

 years ago. At that time considerable areas 

 of unbroken sod still remained. Now the 

 wild prairies have ceased to be a factor in 

 the production of hay. They have given way 

 to cultivated fields and pastures, and the 

 few small unbroken areas occurring here and 

 there are chiefly confined to the small drain- 

 age basins between the hills where moisture 

 interferes with proper cultivation. The 

 standard and other cultivated grasses that 

 have been introduced have been tried with 

 varying success ; the native species vary in 

 quantity and quality in different parts of the 

 State. Several native leguminous plants 

 have more or less value for fodder. The 

 pastures suffer deterioration from overstock- 

 ing and the growth of weeds. The grasses 

 can not endure the close gi'azing and exten- 

 sive trampling to which they are subjected, 

 and die out, and weedy annuals plant them- 

 selves in their places, or the native ragweeds 

 and verbenas spread and occupy the soil. 

 All of these have become so plentiful that 

 farmers note their more frequent occurrence 

 than in former years. In Nebraska the 

 grasses do not grow so luxuriantly season 



