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QUESTIONS FOR MASTERS AND MATES.--NO. 18. 265. When the annual change in the variation is large enough to ma- terially affect the compass on the chart, what is to be done? 266. How would you allow for it if you did not have a new chart? 267. On what line does the compass and chart agree? 268. Describe the course of this line in the lake region. 269. Is an isogonic line a line or an irregular line? 2/0. Is the magneti¢ meridian of a place a straight line or a curved line? 271. What is the difference between an isogonic line and a magnetic mer- idian ? 272. What kind of variation do we have to the east of the line of no vari- ation on the lakes? 273. How do you know when the variation is either easterly or westerly? straight 274. Which variation is increasing and why? 2/5... 3s .the: variation always ..to be found on the chart? 276. Is a magnetic chart compass of much service on the chart? 277. Do you use them? 278. Explain how you get the vari- ation for your courses. Give an ex- ample of it. 279. What variation would you use to the true cotrrse between Whitefish Pt. and Eagle Harbor? Would you make one course or two courses of it? Can you make one course of it? What will your correct magnetic course be between those two points? ANSWERS TO QUESTIONS FOR MASTERS AND MATES--NO. 18. 265. Add or subtract the increase. or decrease as required to the variation for that place. 266. Multiply the amount of yearly change by the number of years the chart was published and add or sub- tract as needed. 267. The line of no variation. 268. Answered in No. 2. Question 28. 269. An irregular line. 270. The magnetic meridian of a place is a straight line. A magnetic meridian is a great circle in whose plane lies the compass needle when. un- affected by deviation, but the meridian of a place is approximately a straight line at the place. 271. An isogonic line merely marks Or passes through those places having an equal amount of variation, while a Magnetic meridian is a_ straight line from the place of observation to the Magnetic pole. © 272, Westerly. "TAE Marine REviEw 273. Take it from the chart. 274. Wly. Because the magnetic pole is moving to the westward around the true pole. 210." Ves, 2/6. They are too small to be of much service. They answer very well for short courses that are entirely within the scope of the equal Var. printed on the chart compass, but are little or no use for long courses where Var. is dif- ferent in amount or name. 277, No: 278. Take the amount of the Var. at each end of the course, add them and divide by 2, apply thismean Var. to the course. Eagle Harbor to Devils Island WSW % W (true) Var. at Devils Is- land 6 degrees Ely. at Eagle Harbor 2 degrees Ely, total 8 degrees Ely. 2)8(4 degrees of 3 pt. Ely. mean Var. Mean C. M:; course Wess 12S. 2/9. Vrue course Whitefish Pr-= Eagle Harbor WNW % W. Var: at Whitefish Pt. 2 Wly. at Eagle Harbor 2 Ely. Asthé line: of no Var, lies mia. way along the course I would make one course of it, The trie course is also the correct magnetic course. NALS. All Canadian lights and fog alarms in Lake Superior will be kept in oper- ation this autumn until Dec. 10, with the exception of Caribou island, which may not be kept in operation later than Dec. 5, subject to weather condi- tions, or early closing of navigation. Mariners must not rely on finding any of these lights in operation later than the dates. above specified for closing. All Canadian lights and fog alarms in Lake Huron, Georgian bay, Lake St. Clair, Lake Erie, Lake Ontario, and connecting waters, will be kept in operation until Dec. 15, excepting Lonely island, Western islands and Red Rock lights, in Georgian bay, which may be closed on Dec. 10 i navigation closes early. : All Canadian lights in the River St. Lawrence will be kept in operation as long as navigation is open, and all gas buoys will be kept at their stations as long as ice conditions udmit, and when it is necessary to remove the buoys before the close of navigation spar markers will be laid down where pos- sible. Js EEE The American Spiral Pipe Works, Chicago, have just issued circular No. 22, showing some of the va and many advantages and ec of Taylor's spiral riveted pipe and forged steel flanges. ried uses conomies 19 MARE ISLAND STRAIT REPORT. The report of the board of engi- neer officers of the United States army and navy concerning the im- provement of Mare Island _ strait gives an estimate of $1,797,000 as the probable cost of the work. This ex- amination was made with a view to deciding the question as to whether it would be more desirable to im- prove 'the facilities for entrance to the Mare Island navy yard as well as to enlarge that yard or whether a new site for a navy yard be chosen. 'The estimate given includes the cost of a self-containing and self-propel- ling dredge which it would require about $125,000 a year to maintain, The recommendation provides that the strait be dredged to a 30-ft. depth with a width of 600 ft. over the bar and up to the turn, a width of 400 ft. from the turn to the receiving ship -- wharf and a width of 1,000 ft. from that point to the north end of the quay wharf; that the dikes within the strait and at the lower end of Mare Island be extended and that the channel in San Pablo 'bay be dredged to a width of 500 ft. and a depth of 30 ft., all depths being the mean low water. He Instructions to the board of civil engineers. referred only to the im- ' provement of the approaches to Mare Island strait from the sea and of the strait itself They did not include an investigation of the suitability of Mare Island and adjacent waters for navy purposes, nor plans for develop- ments of docks and anchorage facili- ties. : oy me The extension of the present dike system and the dredging of the chan- nel are recommended, with the ex- planation that the extended dikes will assist in maintaining the desired depths, together with such additional dredging as may be necessary. _ The plan provides for the dredging of the basin and proposed channel in the strait to 30 ft. at mean low water, and the extensions of the dikes with- total distance of in the strait, a 2,400 ft. eo The removal of the commission rock to'a depth of 20 ft; is recom- mended by the board; also the addi- tion of a dike at the foot of Mare Island, extending down stream 1% to prevent filth being carried with a proviso that it be further extended should condi- it advisable. The esti- of this improvement is miles, into the stream, tions render mated cost $1,007,000.