fig1 shows schematically two coal layers c and c &# 39 ;, a bore hole b with deviating bore holes d , d &# 39 ; and d &# 34 ; leading into layer c , and deviating bore holes e , e &# 39 ; and e &# 34 ; leading into layer c &# 39 ;. at the end of the deviating bore hole chambers f , f &# 39 ;, f &# 34 ;, g , g &# 39 ; and g &# 34 ; have been made by means of a scraping device as described in this specification . after the bore hole has been bored and has been deviated in the coal layer in the way in fig2 it is finished as far as the top of the coal layer with two series of steel casing strings 1 . at various places in these casing strings , sections 2 ( see fig5 ) of other material e . g . &# 34 ; securaloy &# 34 ; can be inserted so as to make it easier later on to be able to deviate to other points in the same coal layer or other coal layers . the sections can be removed chemically or by means of milling . without making use of the latter , one or more windows can be made in the casing strings , too , in order to use the upper part of the cased bore hole again . so as to show that a scraper structure that has been passed through the bore hole indeed can be unfolded laterally in the coal layer , one of the many constructions possible is further described here in brief . in the case drawn ( fig4 ) the scraper structure consists of four sections , which are hingingly attached to each other . they are contracted by pulling cable 4 , which is attached to the lower end of the scraper structure at 5 , and furthermore guidingly attached to half of hinged joints 6 , as can be seen in fig4 . the first section is formed by the underside of the pipe tube 12 . in order to promote the displacement of the scraper structure in the direction of the lower end of the bore hole , the hinges can be constructed springingly in such a way that the stretched condition is temperarily fixed by spring - loaded connections or snap connections . by pulling them cable 8 the scraper structure is folded up again . it will be clear that the choice of the wall - thickness and inner diameter of the hollow closed sections is determinative as to whether the entire scraper structure will scrape in floating , sinking or suspended condition . if , for instance , a cut is made at the upper surface of the coal layer , the underlying coal will , hopefully , be cleaved by the action of the rock pressure , it will then start floating in lumps against the roof formation and either is having the opportunity to move to the entrance of the cased bore hole via the inclined chamber or it has to be moved towards said entrance mechanically or hydraulically . fig4 also shows that the length of the scraper at any moment depends upon its breadth , on the understanding that the apparatus shortens when it is folded further . consequently , primarily , it will not be necessary that the upper view of the chamber to be formed is rectangular . it may also be desirable to make use of several apparatuses with different folding reaches by exchanging them at the surface , so as to exploit the coal layer over its full breadth as well as to initiate the formation of the chamber out of the uncased bore hole in the coal layer . the teeth , knives or other scraping means of scraper structure 3 can be constructed in many ways . their length must be such , however , that they cannot hamper the passage of the scraper structure through the bore hole downwards when the sections are in stretched condition . the scraper structure is connected with the surface by pipes screwed to each other , forming together the entire scraper device . these pipes have a diameter chosen such that a reasonable annular space remains for the coal recovery . the pulling cable emerges through opening 8 into the hollow connecting pipe right over the scraper structure , in consequence of which a buckling of the connecting tube is prevented under tension . it is not possible simultaneously to run in the pulling cable , while running in the scraper structure and connecting pipes for then this cable would be formed by a great number of loose sections connected to each other . as this is but little pratical , the following method is applied in the example : after the scraper structure itself , with the pulling cable attached to it at the outside , has been lowered into the bore hole , the pulling cable is guided into the upper scraping section at the underside of the hollow tube through opening 8 , whereupon the upper end is guided through plate 9 . on this extremity a retainer device 10 is attached of a size sufficiently great to bear on plate 9 , so that the pulling cable cannot be pulled through retainer device 10 . for the sake of simplicity device 10 is shown in fig4 of the drawing as the end of the cable with scraper structure in folded position . it is self - evident that the length is such that when the scraper is in a stretched condition device 10 just bears on plate 9 as shown in fig3 . this retainer device is of such a construction that coming from above and operating from a distance , one can connect to it or disconnect from it an other cable or pull rod at will . after the scraper structure has been let in the bore hole , a cable with the appropriate catching device is then lowered whereupon the connection with the lower section of the cable is brought about . fig4 also shows the circulation holes 13 for circulating the liquid about . this liquid circulates down through the connecting pipes to somewhere near the scraper structure and together with the lumps of coal returns to the surface , via annular space 11 . if the lumps are too large , they can be reduced to the correct size by the scraper or by other mechanical crushers . to this purpose perhaps the apparatus has to be exchanged now and then , involving some round tripping . the coal can be won at the surface by means of vibrating screens and other devices known per se from the ore benefitiation . it will probably be necessary to recondition the liquid from time to time by methods which are known in the field of mining and petroleum industry . during the excavation as the chamber becomes larger the connecting pipes 12 at the surface will have to be lengthened . this may be done by temporarily stopping the activities and screwing together one or more joints of pipes 12 of , for instance , 10 meters length each . close to the surface , the pulling cable may be replaced by pump rods and so - called &# 34 ; polished rod &# 34 ;. the latter passes through a stuffing box placed at the end of the connecting pipe 12 ; connecting pipe and polished rod via an equal tension device are both being suspended from a rotary hook and traveling block that provides for the upward and downward movement . circulating openings are present to circulate the heavy liquid into the connecting pipe . the hoisting device that brings about this upward and downward movement is not drawn but can be a conventional hoisting device , such as is used in the oil industry .