M. Járó - L. Költő szerk.: Archaeometrical research in Hungary (Budapest, 1988)

Prospecting - SŐRÉS László: Geophysical measurements at the site of a Roman homestead at Balácapuszta

Since no data could be obtained for the above-mentioned prism model from theoretical calculations, nor from analogue modelling, the field of a cylinder of similar crosssection was considered instead of the prism of quadrilateral base. The resultant obtained from theoretical calculation of this effect can be seen in Fig. 3, If the distance of the walls lying next to one another is about 2-3 m, their effect does not appear as a protruding peak but as a wide maximum over the walls. The fluctuation of the increased resistivity values is lost in the noise of the measurement, so it is unsuitable for separating the peaks. In this case, it must be considered whether the resultant higher resistivity is the effect of a building, or whether it is attributable to some geological cause. The debris scattered over a larger area may lead to similar types of anomalies. The results of measurements performed over such models is discussed in detail in the appendix. Interpretation of measurements Let us now change to a more detailed evaluation of the maps. The resistivity and conductivity distribution maps of Figure 1 reflect — though not very clearly — the position of the ruins. The two maps are surprisingly similar. The dynamics of direct current resistivity distribution is greater, which can be explained by the fact that it responds more intensively to the high resistivity of the walls. The places of the maxima and the electromagnetic conductivity minima coincide, and even the shapes of the anomalies are similar. The direction of the SE outer wall can be traced very well by the isolines of both maps, and the effect of the building marked with no. V can also be realized. The NE outer wall could not be detected unambiguously, possibly due to its incomplete character. The largest maxima indicate two separate groups of buildings. The maximum marked with 1 draws attention to buildings so far unknown. This is where the phenomenon of the above described deviation appears most intensively. As was discussed previously, this may be due to several reasons. It is possible that the phenomenon is caused by the mosaic or terrazo floors, but it is more likely that it is only the effect of the intact walls reaching deep down. Such a great resistivity contrast was not experienced anywhere else in the area, which suggests the presence of walls preserved in good condition. It can be stated on the basis of maximum no.2 that the walls located there belong to building no. Ill - which is not well known from the excavations performed at the beginning of the century. The maximum no. 3 is the effect of a wall-like building extending over 20 m. A canal built of stone or brick may also be taken into consideration. The slight spots of area no. 4 suggest the presence of buildings much more incomplete and ruined than the previous ones, and nothing more can be told about them on the basis of the measurements. Even so, the orientation appearing on the maps is striking. The sharp maximum no. 5 is the effect of the concrete base of a pole. The effect on resistivity of the excavated buildings no. IV is small; this was to be expected since it could be only very insufficiently reconstructed during the excavation. On the basis of the interpretation map of the residual anomaly, a more definite picture of the area is obtained (Figure 2). The strong anomalies, which can be correlated well, are marked with filled circles, and the weak effects, by empty circles. Two buildings of different directions could be detected at the place of maximum no. 1. They possibly originate in two different building periods — although it is not the task of geophysics to judge this question. The directions of the walls of one of them and those of the walls excavated in the SE corner of the main building strikingly correspond. It