ON IMPROVEMENTS IN MATHEMATICAL INSTRUMENTS. 



53 



ON POTATOES, 



RY THOMAS ANDREVV KNIGHT, ESQR. 



Transactions of HorticuUural societ_v, Vol. 1, part 4. 



From experiments whicli have been 

 made on the potato, it is inferred, that 

 when a plant affords either seeds or blos- 

 soms, a diminution of tubers, or an in- 

 creased expenditure of the richness of 

 the soil, must necessarily take place; and 

 Mr. Knight is satisfied from his own 

 'practice, that the crop is increased by de- 

 stroying the fruit-stalks, and immatured 

 blossoms, as soon as they appear, and he 

 had thought that very considerable advan- 

 tages would arise if varieties of a suffici- 

 ently luxuriant growth, and large pro- 

 duce for general culture, could be formed, 

 which would never produce blossoms; 

 and such, he has the gratification to find, 

 may be readily obtained. And by shift- 

 ing his varieties, so as to make them ripen 

 earlier in each succeeding year, he has no 

 doubt of having completely established a 

 potato, which will produce tubers without 

 either fruit or blossom. — Retrospect. 



Obse7'vations. — By mowing off the 

 tops of potatoes, so as to prevent the stem 

 and blossoms from attaining maturity, is 

 recommended. 



.MR. SCHMALCALDER'S PATENT FOR CER- 

 TAIISr IMPROVEMENTS IN MATHEMATICAL 

 INSTRUMENTS. 



March 1812, Rep. Arts. 129. 



On the edge of the mariner's compass, 

 theodolite, or other instrument for meas- 

 uring angles of azimuth, Mr. S. places a 

 three-sided prism; this produces a single 

 reflection, and enables the observer to 

 read the divisions on the card, at the stime 

 time, by raising his eye partly above the 

 angular edge of the prism, he sees the 

 subject of observation by direct vision. 

 In this manner the line of collimation be- 

 comes the index to the card divisions, and 

 the azimuth or bearing may be taken and 

 read off at one observation. 



By the application of a four sided pyr- 

 amid, on the same principle, to a plumb- 

 line, spirit-level, or the divisions of a the- 

 odolite, or other instrument, Mr. S. is 

 enabled to see the object by direct vision; 

 the position of the plumb-line, etc., by 

 means of one reflecting or inciii!^d sur- 

 face, and to read off the divisions by the 

 other reflecting surface. 



The adaptation of these prismatic re- 

 flectors to the telescope, Hadley's sextant, 

 and similar instruments, enables an obser- 

 ver to obtain the angles of azimuth, and 

 altitude, without the usual necessity of 

 assistants. Where a magnifying power is 

 required, Mr. S. produces it, by making 

 certain surfaces of the prism convex. 



ON A METHOD OF FREEZING AT A 



DISTANCE. 

 BY WILLIAM HYDE WOLLASTON, M. D. 



Sec. R. S. Piiil. Trans, lor 1813. 



If an attempt were made to freeze 

 water by mere evaporation in the vacuum 

 of an air pump, (Ur. W. observes,) the 

 receiver must be of large dimensions in 

 proportion to the quantity of water em- 

 ployed, otherwise its capacity would set 

 too confined a limit to the quantity of va- 

 pour that will rise, and consequently to 

 the degree of cold produced. Accord- 

 ing to the commonly received estimates 

 as to the respective quantities of heat in 

 ice, water, and steam, 33 grains of water 

 at 62° must lose about 5 grains by evapo- 

 ration, in order to convert the remainder 

 into ice, (making no allowance for the ac- 

 cession of heat from the surrounding bod- 

 ies,) and as water expands to ISOO times 

 its former bulk when it assumes the gas- 

 eous state, these 5 grains require a dry 

 vacuum of 5 + 1800 == 9000 grains of 

 water. 



To avoid the necessity of so large a 

 vacuum, Mr. Leslie has most ingeniously 

 employed an extensive surface of some 

 substance that strongly absorbs and con- 

 denses the vapour of water, (sulphuric acid 

 in preference to any other,) which, by ex- 

 tracting from the receiver the aqueous va- 

 pour as fast as formed, keeps up a vacuum 

 within it, and thus allows the congelation of 

 a large quantity of Vv'ater in a moderate 

 space. Dr. W. has employed another way 

 of applying the same principle of pre- 

 serving a vacuum round the water to be 

 frozen in the little apparatus here describ- 

 ed. This is no other than the common 

 glass toy called ihe inilse glass, and con- 

 sists of a bulb of glass blown at each end 

 of a piece of a glass tube, and bent at 

 right angles to the tube. 



One of the bulbs is half-filled with 

 water, and the other hermetically sealed 

 at the moment that the whole is kept fill- 



