26o 



SCIENCE. 



[Vol. XXI. No. 536 



they might have upon their surface a sufficient amount of poison 

 to produce injurious effects, would seem above suspicion. 



The results obtained from spraying various fruits with a com- 

 bined fungicide and insecticide in 1892 convinced the writer that 

 too great care cannot be taken in the use of these poisons upon 

 all crops, any exposed portions of which are edible, and that in 

 no case should they be used within one month of the time of 

 ripening, while an interval of six weeks to two months will be 

 preferable. The fruits experimented upon were strawberries, 

 raspberries, currants, gooseberries, cherries, and pears. The ex- 

 periment was conducted in the same manner with all of the 

 fruits, and when ripe they were analyzed and tested for arsenic 

 and sulphate of copper. The spraying was done about as in ordi- 

 nary practical work, except that it was rather more thorough, 

 the amount used being perhaps double that generally employed. 

 Except that the raspberry and strawberry retained rather more 

 of the poison, the results were quite similar, and those obtained 

 with two of the fruits will answer for all. 



Gooseberries sprayed June 18, 39, July 8, and 23 with Bor- 

 deaux-mixture (copper sulphate, 3 pounds ; lime, li pounds ; water, 

 33 gallons) and London purple (1 pound to 300 gallons), using 

 one-half gallon of the mixture to a very thick, full row two rods 

 long. One pound of fruit gathered Aug. 3 gave, on analysis. 

 .0365 grains of arsenic and .355 grains of copper sulphate. In 

 making the analysis, the fruit was first washed in ten per cent 

 hydrochloric acid, and the amounts Of arsenic and copper sulphate 

 thus abstracted were, respectively, .0203 grains and .208 grains, 

 after which there remained of each .0163 grains and .147 grains. 



Fruit from another row that had been sprayed in a similar 

 manner, except that the Bordeaux- mixture was made from the 

 usual formula (copper sulphate, 6 pounds ; lime, 4 pounds ; water, 

 33 gallons), gave of arsenic .0723 grains, and of copper sulphate 

 .62 grains, from one pound. In each case the last spraying was 

 eleven days previous to the date of picking. 



The pears were sprayed with the same mixture as the first lot 

 of gooseberries, on June 15, July 7, 21, and Aug. 7, and were 

 gathered and analyzed Sept. 6, or thirty days after the last appli- 

 cation. The result from one pound of fruit gave, of arsenic .0089 

 grains, and of copper sulphate .0745 grains. 



The above analyses were made under the direction of Dr. R. C. 

 Kedzie, chemist of the Michigan State Experiment Station. 



Attention is called to the fact that only about one-fifth as much 

 copper sulphate was found upon the pears thirty days after spray- 

 ing as upon the gooseberries gathered eleven days after receiving 

 the last application, also that with a weak solution as compared 

 with a strong one, the amount both of copper and arsenic remain- 

 ing upon the fruit was reduced in about the same ratio as the 

 strength of the mixture used. 



This certainly emphasizes the advice previously given, (1) to 

 use a solution as weak as will secure freedom from disease, and 

 (2) cease spraying with all poisons at least one month before the 

 fruit ripens. 



LIGHTHOUSE ILLUMINANTS. 



BT WM. P. ANDERSON, CHIEF ENGINEER OF MARINE DEPARTMENT, 

 OTTAWA, CANADA. 



In Science for Feb. 6, 1885, a sketch was given of the progress 

 of lighthouse illumination in Great Britain and Ireland, together 

 with a short description of the strongest lights and apparatus 

 utilized up to that time. Since that article appeared the conflict 

 between the advocates of electricity, mineral oil, and gas, re- 

 spectively, has not decreased, nor has any settlement satisfactory 

 to all parties yet been reached. The matter has on several occa- 

 sions been brought before the Imperial Parliament, and in Feb- 

 ruary last some further correspondence on the subject was laid 

 before the House of Commons. 



A consideration of some of the points lately elicited will be an 

 interesting addition to Mr. Kenward's notes on lighthouse appar- 

 atus in Science for April 21 last. 



The lighthouses of the United Kingdom are under divided 

 control: the English lights are managed by the Trinity House, 

 the Scotch lights by a board of commissioners, and the Irish 



lights by a separate commission ; all under the general direction 

 of the Government Board of Trade, and each anxious to main- 

 tain lights of the highest efficiency, almost regardless of cost. 



The English authorities, from the observations made in 1885, 

 are satisfied of the superiority of electric arc-lights where the 

 highest possible power is required, and consider oil-lights the 

 cheapest and most easily managed for ordinary purposes. The 

 Scotchcommissionersendorse this view of the case; but the Irish 

 board seems to favor the use of illuminating gas. 



The chief opposition to the decision of the English Trinity 

 House appears to be instigated by Mr. John R. Wigham of Dub- 

 lin, the inventor of the gas system. He claims that he did not 

 get fair play in the trials of 1885, because a rule was adopted re- 

 stricting the size of the lenses and lanterns within limits that 

 prevented him from obtaining the best results from his gas-lights. 

 Since that time he further claims that by enriching common gas 

 with hydrocarbon a greater amount of light can be obtained from 

 it than from the richest cannel-coal gas. Actual experiments 

 have shown that cannel coal gas has an illuminating power of 38 

 candles, nearly double that of ordinary Newcastle-coal gas, 16 

 candles. By passing the ordinary gas through the vapor of solid 

 napthaline, or albo-carbon, a perfectly safe and inexpensive ma- 

 terial, it is enriched with hydrocarbon to such an extent as to 

 give double the illuminating power of cannel gas. He also sug- 

 gests, as an improvement in lighthouse illuminatjion, placing 

 lenses so as to form a quadrilateral or trilateral figure, which 

 would permit the use of lenses of much larger illuminating sur- 

 face and of much longer focal distances than is possible with the 

 6, 8 or even 16-sided lenticular apparatus heretofore used, thereby 

 immensely increasing the illuminating power of the lighthouses. 



Mr. Wigham has had a lens of long focus made, with a bulls- 

 eye or central portion 19 inches in diameter, and two concentric 

 rings, one 4 and the other 4J inches wide, giving a total diameter 

 of 36 inches, all in one piece. This is surrounded by a belt of 

 prisms 3 feet 10 inches wide, consisting of ten rings, outside of 

 which is a third portion consisting of eight rings of totally re- 

 flecting prisms, partially surrounding the second portion, so as 

 to complete a lens about 10 feet 10 inches wide by about 8 feet 

 high. In the focus of this lens is placed an " intensity " burner 

 composed of 148 fish-tail jets, grouped to burn the enriched gas. 

 which, when lighted, forms a solid flame of 14 inches diameter 

 by 6 inches high. The illuminating power of the burner is cal- 

 culated to be about 8,500 candles, which should give an actual 

 intensity of light through the lenses of about 2 300,000 candles. 

 Experiments made with this apparatus showed splendid results 

 at a distance of 6i miles. In full moonlight the beam casta strong 

 shadow, and was very large and dazzlingly bright, reducing a 

 neighboring first-order flxed light to what seemed by comparison 

 a remote and feeble glimmer. 



The case for and against gas as a lighthouse illuminant seems 

 to be as follows: Its advantages are facility in increasing or de- 

 creasing the power of the light to suit the various states of the 

 atmosphere, and also speed and sharpness in eclipsing lights by 

 cutting off the supply of gas, and thus occulting them while at 

 the same time saving the illuminant; as well as the fact that 

 where gas is used for illumination it can be utilized at a minute's 

 notice to operate a gas-engine in connection with a mechanical 

 fog-alarm, while with any other source of power delay must 

 occur in putting the fog-alarm into operation. It is further 

 claimed that the large size of the gas-flame, giving an unusual 

 number of extra-focal rays, has a better effect in illuminating a 

 large area of fog, and consequently makes the light more readily 

 visible. 



The weak points of gas are the difficulty of manufacturing it 

 at some isolated stations, and also the necessarily large size of 

 the flame, which involves the use of very large lenses, and a 

 long focus, to prevent a wasteful distribution of extra-focal light. 



The arrangement of illuminating apparatus proposed by Mr. 

 Wigham for a most powerful light is a battery of four giant 

 lenses, surrounding a central burner, intensified by having simi- 

 lar lenses with additional burners arranged one over the other in 

 three tiers, or "in triform." To accommodate such an apparatus 

 would require a lantern with glazing at least 20 feet in diameter 



